D.B. is a 30 yr-old longshoreman who had pectus excavatum involving the lower 75% of the anterior chest since infancy, a condition that became worse during his adolescent growth years and persisted into adulthood with increasing symptoms (see Fig. 2A). The heart sounds were displaced toward the left chest, and x-rays showed the heart to be shifted markedly into the left chest. No cardiac murmurs were audible. The lungs were clear on auscultation, and with deep inspiration, the depression became more severe.
Although the patient jogged 3 miles·d−1 3 d·wk−1 at moderate intensity over the last 4 yr, D.B. experienced frequent episodes of pain in the lower anterior chest, breathlessness, and reduced stamina when performing activities of daily living. At the time of diagnosis, he weighed 88.2 kg and was 1.96 m tall. D.B. was self-referred to UCLA Medical Center to be evaluated for surgical correction of his chest wall deformity. Approval was given by the University of California, Los Angeles Human Subject Protection Committee for analysis and reporting of this clinical data. Additionally, the patient signed an informed consent before the initial physiological assessments.
Measurement of severity index.
A severity index, based on measurements obtained from CT scans of the chest, was determined for the patient by the co-investigator (EWF). The width of the chest was 21.9 cm, and the distance between the sternum and the spine was 5.9 cm: thus, D.B. had a severity index of 3.7.
Pulmonary function testing.
Spirometry was performed in the seated position with a nose clip applied after the subject had rested for at least 10 min. Testing was performed in the Pulmonary Function Laboratory at UCLA Medical Center by certified pulmonary function technologists using equipment and procedures that meet the American Thoracic Society criteria for the standardization of spirometry (2). Forced expiratory (e.g., FEV1, FVC) maneuvers were performed in triplicate with the minimal requirement of at least three “satisfactory” maneuvers and the best two maneuvers meeting reproducibility criteria within 200 mL (or 5%). Spirometric measures were repeated, if necessary, up to a maximum of eight times in an attempt to achieve both satisfactory and reproducible results. The spirometer was calibrated using a precision-calibrated 3-L syringe. All values were corrected to BTPS, using an internal thermometer for temperature measurement. The best FVC and FEV1 measurements were reported.
Ventilatory capacity was measured as the maximum voluntary ventilation (MVV). The MVV maneuver was performed in the seated position with a nose clip applied. The subject was asked to breathe through a flow transducer as deeply and as rapidly as possible for 12 s. The level of ventilation was expressed in liters per minute and corrected to BTPS. MVV maneuvers were performed in triplicate, and the highest value was used as a measure of ventilatory capacity.
Subdivisions of lung volume were measured by helium dilution, using procedures in accordance with recommendations of the American Thoracic Society/European Respiratory Society and the British Thoracic Society (6). Reported values included the functional residual capacity (FRC), residual volume (RV), and total lung capacity (TLC). The three highest acceptable and reproducible values for TLC were recorded and the mean value calculated. Reproducibility was defined as the two smaller of the three TLC being within 10% of the largest one. Calibration of flow, volume, and pressure transducers was performed in accordance with the manufacturer’s specifications.
Single-breath diffusing capacity for carbon monoxide (DLCO) was measured according to the standard technique recommended by the American Thoracic Society using equipment that meets minimum ATS requirements (1). Before each test session, leak testing was performed, and the accuracy of the volume measurements was checked using a precision-calibrated 3-L syringe. The linearity of the helium and carbon monoxide analyzers and the accuracy of the timing device in the DLCO apparatus were verified. Measurements were performed with the subject seated and wearing a nose clip. At least two acceptable tests, as defined by the ATS, were performed and the mean value calculated (uncorrected for hemoglobin). Reproducibility was defined as two values within 10% of each other or within 3 mL CO·min−1·mm Hg−1 of the mean value. Peripheral venous hemoglobin and carboxyhemoglobin were measured using a CO-oximeter before performance of the DLCO test. These values were used to adjust the measured values of DLCO using the method of Cotes (12). The HbCO correction was used only if HbCO was elevated. Both mean DLCO and mean VA (alveolar volume) were recorded and DL/VA calculated.
The pulmonary function test results were expressed both as measured values and as percentages of gender-specific reference values using the regression equations of Crapo et al. for spirometry (14), Becklake for subdivisions of lung volume (4), and Cotes et al. for single-breath DLCO (13).
Maximal exercise performance was assessed using an incremental exercise protocol on a cycle ergometer (Ergoline 900S; SensorMedics Corp., Loma Linda, CA). The power output was continuously increased in ramp fashion by computer control. The exercise duration for the ramp phase was 8–12 min as suggested by Buchfuhrer et al. (8). The subject wore a nose clip and breathed through a mouthpiece (2700; Hans Rudolph, Kansas City, MO). Minute ventilation (V̇E) was measured using a mass flow meter, and expired fractional concentrations of oxygen and carbon dioxide were continuously monitored by paramagnetic oxygen analyzer and nondispersive infrared CO2 analyzer, respectively (2900; SensorMedics Corp.). Oxygen uptake (V̇O2) and carbon dioxide output (V̇CO2) were calculated breath-by-breath using standard algorithms. Breath-by-breath data were presented as a five-breath rolling average. After a period of stabilization at rest, the subject performed unloaded pedaling (i.e., 0 W) for 3 min followed by the ramp increase in power output (i.e., 20 W·min−1). The subject was asked to maintain a cycling cadence of 60 rev·min−1. The ramp power output increased until the subject reached volitional fatigue. After such time, a cool-down period with no resistance was performed until the heart rate (fc) was near the rate at unloaded pedaling. A 12-lead electrocardiogram was obtained every 2 min throughout exercise, and fc rate was continuously recorded (Model Q5000; Quinton, Seattle, WA). Peripheral oxygenation was monitored by a pulse oximeter (Biox 3740; Ohmeda; Helsinki, Finland) attached to a finger. Immediately after exercise termination, the subject was asked to give a rating of perceived exertion (RPE) using the Borg scale (11) and to score breathlessness using a 100-mm visual analog scale with standardized instructions.
Maximum oxygen uptake was compared with standard prediction equations (11). V̇O2θ was determined by noninvasive gas exchange measurements using the method of Beaver et al. (3) in conjunction with analysis of the ventilatory equivalents (i.e., V̇E/V̇O2 and V̇OE/V̇CO2) and end-tidal gas tensions (i.e., PETO2 and PETCO2) for oxygen and carbon dioxide. This method relies upon the detection of excess CO2 derived from bicarbonate buffering of lactic acid and has been found to have a correlation coefficient of 0.95 when compared with blood lactate analysis (23). Both V̇O2max and V̇O2maxθ were reported as absolute values in liters per minute. To evaluate its normalcy, V̇O2θ was also reported as percent of reference value for V̇O2max. Additionally, we reported the maximum power output (&U1E86;max) achieved which was measured in Watts.
V̇O2 kinetics with exercise.
The kinetic response of V̇O2 to a step change in power output was determined from a preliminary submaximal testing protocol performed before incremental testing to familiarize the patient with the cycle ergometer. The exercise protocol consisted of 6 min at a power output of 15 W, followed by 6 min at a steady-state power output (&U1E86;ss) calculated to elicit 40% of reference V̇O2max, then a further 6 min at a power output of 15 W. Throughout this protocol, V̇O2 was measured using a mixing chamber technique. V̇O2 and cumulative V̇O2 were calculated every 20 s and plotted as functions against time. τV̇O2 was calculated for both the on-τV̇O2 (e.g., 15 to &U1E86;ss W) and the off-τV̇O2 (e.g., &U1E86;ss to 15 W) from the horizontal displacement of the two components of this plot that define the lower power output phases using a previously described geometric analysis (9,10). This protocol was purposefully designed to be submaximal and below V̇O2θ.
The highly modified Ravitch repair (HMRR) surgical technique used with this patient was an extensive modification of that described by Ravitch (31) with less cartilage resection. A transverse curvilinear incision was made midway between the nipples and costal margin extending from mid-nipple line bilaterally. Limited skin flaps were elevated over the pectoralis muscles using needle point electrocautery to minimize blood loss. The pectoralis major muscles were reflected laterally from attachments to the sternum and costal cartilages, and the abdominal muscles were mobilized from the lower costal cartilages. The perichondrium was incised on the mid-anterior surface of the lower four to five costal cartilage bilaterally, extending from the costochondral junction to the sternum. The abnormal costal cartilages were resected subperichondrially, carefully preserving the perichondrium. The xiphoid was detached from the sternum and the intercostals muscles and perichondral sheaths of the involved ribs were transected from the sternum. The lower retrosternal space was mobilized, the pleura were incised on the right side of the mediastinum, and a small chest tube was inserted. A transverse anterior wedge osteotomy of the sternum was made at the level where the sternum depresses posteriorly, and the posterior table of the sternum was gently fractured without displacement and then elevated to the desired position. Nonabsorbable sutures were placed through the anterior table of the sternum across the osteotomy and a stainless steel (Adkins) strut (Baxter Healthcare Corp., Operating Room Division, McGaw Park, IL) was placed across the lower anterior chest to support the tip of the sternum and was attached to the appropriate rib on each side with wire. The xiphoid and perichondral sheaths were sutured back to the sternum and the pectoralis and abdominal muscles were sutured together over the sternum. The skin was closed with subcuticular absorbable sutures and steristrips or staples.
Thorough homeostasis was achieved with electrocautery, and the wound was copiously irrigated with antibiotic solution (i.e., cefazolin) throughout the operation. The chest tube was removed within 24 h after operation, intravenous antibiotic cefazolin was given for 3 d, and an oral antibiotic was given for 4 additional days. Postoperative pain was remarkably mild and was controlled with intravenous analgesics for the first 2 postoperative days and by oral medications thereafter.
Removal of sternal support bar.
The Adkins strut was removed as an outpatient procedure under light general anesthesia 6 months after the repair. The tip of the bar was identified with the portable fluoroscopic unit. A small skin incision was made and the bar was withdrawn with gentle traction. The entire procedure took approximately 30 min, and the patient was observed in the recovery room for 2 h then discharged.
Both pulmonary function and exercise testing protocols were repeated 6 months after corrective surgery before removal of the Adkins strut. It has been our experience that the strut does not impair pulmonary function or exercise testing indices (22). During the 6 months after corrective surgery, the patient maintained an exercise regimen, jogging 30 min·d−1 4 d·wk−1 at moderate intensity followed by 30 min of circuit weight training (six exercises, 15–20 repetitions, with 30-s rest between exercises, repeated three times) for the major muscle groups.
Pulmonary function tests.
As shown in Table 1, FEV1 and MVV, increased by 13.0% and 32.3%, respectively, after corrective surgery. However, other pulmonary indices such as FVC, TLC, and DLCO did not change dramatically. Therefore, we concluded that pectus excavatum affected the patient’s pulmonary function when performing forced maneuvers but did not affect the overall pulmonary function. This is further corroborated by the normal percent of reference value for each index.
The preoperative observed V̇O2max was 3.03 L·min−1, which corresponded to 90% of the predicted V̇O2max. V̇O2θ was detected at an oxygen uptake of 1.30 L·min−1, which corresponded to 39% of the predicted V̇O2max. D.B. achieved a &U1E86;max of 245 W. Six months after corrective surgery, D.B. had an observed V̇O2max of 3.27 L·min−1, which corresponded to 96% of the predicted V̇O2max. V̇O2θ was detected at an oxygen uptake of 1.70 L·min−1 which corresponded to 50% of the predicted V̇O2max. Also, he achieved a &U1E86;max of 283 W (see Table 2).
The δV̇O2/δ&U1E86; slope is consistent in healthy subjects (10.3 mL·min−1·W−1 ± 1.0 mL·min−1·W−1). D.B. was observed to have a slope of 11.1 mL·min−1·W−1 before surgery and a slope of 10.9 mL·min−1·W−1 6 months after corrective surgery. Both values are within the 95% confidence interval of 8.3 to 12.3 mL·min−1·W−1. The observed normalcy of δV̇O2/δ&U1E86; argues against severe impairment of oxygen utilization by skeletal muscles.
We examined the kinetic response of oxygen uptake with the onset of moderate constant load exercise from a baseline of pedaling at a low power output (on-τV̇O2) as well as the response on reversion from moderate constant load exercise to pedaling at a low power output (off-τV̇O2). In normal subjects predicted values are approximately 30 s with on-τV̇O2 and off-τV̇O2 being equal (34). In our patient, preoperative on-τV̇O2 was 46.8 s and off-τV̇O2 was 46.5 s, respectively. Six months after the corrective surgery, on-τV̇O2 was 33.6 s and off-τV̇O2 was 30.3 s.
Oxygen pulse (V̇O2/fc), an indirect measure of cardiac stroke volume, was lower before corrective surgery than after corrective surgery (16.2 mL vs 18.5 mL). This increase of 14% may be explained by increased cardiac output after relief of cardiac compression. Additionally, the observed fcmax before surgery was 187 beats·min−1 (98% of the predicted fcmax). After corrective surgery, the observed fcmax was 177 beats·min−1, which corresponded to 93% of the predicted fcmax. The RPE, as measured by the Borg scale, was consistent with the observed cardiovascular response. D.B. exhibited cardiovascular limitation with an exaggerated cardiovascular response pattern, as demonstrated by a steeper relationship between fc and V̇O2, preoperatively. After corrective surgery, the relationship between fc and V̇O2max was normal, reflecting a slope often seen in aerobically trained individuals (see Fig. 3). D.B. perceived the test, as measured by RPE, to be more difficult before surgery when compared with 6 months after corrective surgery (18 vs 15). It should also be noted that the patient was no longer exhibiting a resting tachycardia and had a 20.0% decrease in resting fc after corrective surgery (105 vs 85 beats·min−1).
We also examined the ventilatory and gas exchange responses to maximal exercise in D.B. Preoperative maximum ventilation (V̇Emax) was 108 L·min−1, which corresponded to 109% of ventilatory capacity as measured by MVV. This represents a ventilatory reserve of −9.0 L·min−1. However, after corrective surgery, V̇Emax was 99 L·min−1, which corresponded to 79% of ventilatory capacity as measured by MVV. This represents a ventilatory reserve of 32 L·min−1. Therefore, D.B. exhibited ventilatory limitation to exercise before corrective surgery but did not exhibit ventilatory limitation postoperatively. Maximum tidal volume (V̇Tmax) was 2.57 and 2.87 L before and after surgery whereas the maximum respiratory frequency (fRmax) was 42 and 38 before and after surgery, respectively. Thus, the ventilatory response pattern for D.B. was normal as judged by these parameters preoperatively but improved postoperatively. Gas exchange mechanisms were normal as judged by ventilatory equivalents and end-tidal gas tensions at V̇O2θ (see Table 3). The patient’s perceived breathlessness score was higher before surgery when compared with 6 months after corrective surgery (69 vs 34). Peripheral oxygenation was normal throughout the exercise test before and after corrective surgery as judged by pulse oximetry (94% vs 95%).
Pre- and postoperative measures of cardiorespiratory performance on patients with pectus excavatum have been conducted as early as 1951 (7). However, little is known about the physiological limitations that may exist in patients diagnosed with this condition. In the medical community, the degree of physiological impairment caused by pectus excavatum is a topic of debate with some investigators who support the utility of surgical correction (20,26) and others who believe that correction has more esthetic than physiological benefits (24,35). To address these issues, the current study examined the effect of pectus excavatum on cardiorespiratory outcomes to exercise in a patient before and after corrective surgery.
Preoperative pulmonary function values in D.B. were in the low normal range without abnormalities in breathing mechanics. This finding is consistent with other studies (35). We did observe a large percent improvement in the postoperative FEV1 and MVV values in our subject. We believe that these postoperative changes result from a combination of increased chest wall compliance, optimized working length of respiratory muscles, and better patient effort. Our observation of patients with pectus excavatum has been that a level of apprehension exists when they perform pulmonary function maneuvers. Many patients comment about the discomfort they experience in their chest when asked to exhale maximally. Notwithstanding, the percent of reference for preoperative pulmonary indices were in the normal range.
The ventilatory response to maximal exercise improved after surgery. This finding is consistent with other studies that have reported improvements in V̇Emax at V̇O2max (33). Similar to other studies (5), we found normal breathing patterns as measured by V̇Emax, V̇Tmax, and fRmax before and after corrective surgery. Additionally, gas exchange, as measured by ventilatory equivalents and end-tidal gas tensions at V̇O2θ, was normal before and after corrective surgery.
Our patient’s V̇O2max increased by 7.9% after corrective surgery. More interestingly, the preoperative V̇O2θ value was 39% of the predicted V̇O2max. V̇O2θ is defined as the level of exercise above which aerobic energy generation is supplemented by anaerobic mechanisms with an accumulation of lactic acid as a by-product. This is clinically relevant, because values less than 45% are considered to be a sign of deconditioning or cardiovascular impairment. Because D.B. had a habitual exercise regimen, it is unlikely that his low V̇O2θ was related to deconditioning. Therefore, due to the cardiac compression brought about by pectus excavatum, D.B. had a greater reliance on anaerobic mechanisms to generate energy (i.e., ATP) for muscle contraction. This is unusual, because studies have clearly demonstrated, using serial blood lactic analysis, that with aerobic training, an individual delays the onset of their lactic threshold (i.e., V̇O2θ) (16). Future studies may benefit from examining the blood lactic profile of pectus excavatum patients during incremental exercise testing. D.B.’s postoperative V̇O2θ value was 50% of the predicted V̇O2max. Therefore, although the patient’s habitual exercise regimen remained consistent pre- and postoperatively, V̇O2θ increased by 30.8% merely due to surgical correction. This may be explained by the absence of cardiac compression (see Fig. 2B). As a result, our patient was also able to increase his &U1E86;max by 15.5%.
The measurement of τV̇O2 is important because along with V̇O2max, V̇O2θ, and δV̇O2/δ&U1E86;, it is one of the fundamental parameters of aerobic fitness. Whipp et al. (34) reported a normal value for τV̇O2 in apparently healthy individuals of 35 s with a standard deviation of 5 s. It is important to note that this measure included a delay time after the onset of exercise from a resting baseline before fitting the data with an exponential function. Traditionally, τV̇O2 has been assessed using multiple exercise transitions to minimize the variability of breath-by-breath measurements before reliable exponential curve fitting could be undertaken. Thus, the use of τV̇O2 for clinical assessment is difficult, if not impractical. Through the use of geometric analysis (9,10) and mixing chamber technology, we were able to measure both on-τV̇O2 and off-τV̇O2 in our patient in a single exercise session as part of his pre- and postoperative evaluation. The preoperative values for on-τV̇O2 and off-τV̇O2 were prolonged when compared with expected normal values. This prolongation of on-τV̇O2 and off-τV̇O2 in our patient may be due to central cardiac compression as a result of pectus excavatum. Merely due to the operation, we observed a decrease of 13.2 and 16.2 s for on-τV̇O2 and off-τV̇O2, respectively.
The δfc/δV̇O2 is the slope of the relationship between heart rate and V̇O2 during incremental exercise. This slope is related both to stroke volume and the difference in oxygen content between arterial and mixed venous blood. δfc/δV̇O2 is also the reciprocal of the asymptotic oxygen pulse (V̇O2/fc) that is a measure of cardiovascular efficiency with units of milliliters per beat. Thus, V̇O2/fc is closely related to cardiac stroke volume (SV) and can be used to estimate SV at various stages of incremental exercise testing (11). In our patient, we observed a preoperative V̇O2/fc value of 16.2 mL, which was 91% of predicted. After corrective surgery, we observed a V̇O2/fc value of 18.5 mL, which corresponded to 108% of predicted or a 14.0% increase. This result is similar to Haller and Loughlin (26), who studied 16 pectus excavatum patients and found a 12.2% increase in V̇O2/fc after corrective surgery. The improvement in V̇O2/fc indicates that cardiac compression is an important factor related to symptoms of fatigue in pectus excavatum. Our finding is also consistent with Morshius et al. (30), who studied 35 pectus patients before and 1 yr after corrective surgery and found a significant increase in V̇O2/fc after corrective surgery. The investigators did not state whether subjects were physically active during the 12 months after the surgery. Thus, the improvements in V̇O2/fc may be a result of physical conditioning, or corrective surgery, or a combination of both.
Our study examined a single patient before and 6 months after corrective surgery, and differs from other case study reports on pectus excavatum in three ways. First, we controlled for the patient’s habitual exercise activity before and after the operation. Therefore, his postoperative improvement relates to the changes effected by the surgical procedure. This contradicts studies that have found no change or a decrease in aerobic capacity after corrective surgery. It should be noted, however, that studies examining postoperative cardiorespiratory changes have not controlled for the patient’s habitual exercise history. This raises the question, “Did the patient’s exercise regimen change after corrective surgery?” If the answer is “yes,” then the reported findings may be questionable. This is a key variable to hold constant in future studies. In our experience, we have observed patients who refrain from their habitual exercise regimen for fear of displacing the Adkins strut. This introduces a level of deconditioning, which may explain why some studies find reduced cardiorespiratory function when compared with preoperative values.
Second, we evaluated central cardiac performance by examining V̇O2/fc and τV̇O2. By having the patient continue a similar exercise regimen postoperatively we were able to control for level of fitness. As a result, we saw a 14.0% increase in V̇O2/fc and a reduction of 28.2% and 34.8% for on-τV̇O2 and off-τV̇O2, respectively, after surgery. To our knowledge, no other studies have reported τV̇O2 values in this population pre- and postoperatively. If these findings are supported by a large prospective study, it would strengthen the argument that pectus excavatum limits central cardiac function despite the patient’s level of aerobic fitness.
Third, the surgical technique used on this patient has been found to be superior when compared with other less invasive techniques. Fonkalsrud et al. (19) recently compared the HMRR with the minimally invasive repair of pectus excavatum (MIRPE), which has gained wide acceptance during the last 6 yr. The MIRPE requires insertion of a convex steel bar under the sternum through small bilateral thoracic incisions. The steel bar is inserted with the convexity facing anteriorly, and when it is in position, the bar is turned over with heavy pliers to force the sternum outward. Fonkalsrud et al. (19) found that the MIRPE resulted in a number of complications: a) six reoperations, b) eight rehospitalizations, and c) six bar displacements (flipped). None of these complications were reported using the HMRR. Furthermore, the mean length of hospitalization was 6.5 d using the MIRPE and 2.9 d using the HMRR. Importantly, the mean time to bar removal was 24 months using the MIRPE and 6 months using the HMRR.
Symptoms from pectus excavatum are recognized infrequently during early childhood, and most patients are therefore advised by well-intentioned pediatricians that: a) the deformity will improve with age; b) that surgical repair is dangerous, minimally effective, and unnecessary; and c) the malformation produces few symptoms and is primarily a cosmetic problem. It is for these reasons that the present managed care environment, HMOs, are increasingly reluctant to authorize corrective surgery for pectus excavatum. Ravitch (32) stated, “… in occasional young adults with uncorrected pectus excavatum, the symptoms may progress to severe incapacity with exercise intolerance, tachycardia, and cardiac failure, all of which may be dramatically improved by surgical repair.” The information derived from this case study supports the opinion that corrective surgery for pectus excavatum may alleviate the impaired ventilatory and cardiorespiratory performance seen preoperatively.
The study was supported in part by the UCLA Children’s Fund. We also thank C. Cooper, M.D., for his assistance.
Selected results from this manuscript were presented at the 49th Annual Convention of the American College of Sports Medicine, St. Louis, MI, May 28 to June 1, 2002.
Note: Data were collected while Mr. Malek was a research associate in the David Geffen School of Medicine at UCLA.
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