Slow, controlled breathing has been shown by cross-spectral techniques to potentiate arterial baroreflex control of heart rate. However, crucial aspects of the effects of slow breathing on the arterial baroreflex remain unsettled, namely whether the major function of the arterial baroreflex (i.e. the control of blood pressure) is also potentiated and whether baroreflex function is differentially modulated according to the age of the individual.
To examine the bradycardic and depressor responses to selective carotid baroreceptor stimulation by the neck chamber technique (−15 and −30 mmHg neck suction) and the cross-spectral R–R interval/systolic blood pressure relationship (α index).
In 24 resting, supine healthy male volunteers (aged 19–66 years, mean ±SEM 37.5 ± 3.19 years), blood pressure (Finapres), R–R interval (electrocardiogram) and ventilation (impedance) were recorded continuously. Both assessments were performed during spontaneous breathing and during 6 cycles/min controlled ventilation in random order.
The depressor and bradycardic responses to neck suction were significantly larger during slow breathing than in spontaneous breathing (+32 and +85%, respectively; both P< 0.01). The α index was also significantly larger during slow breathing (+62%; P< 0.01). Even after the volunteers were divided into older (> 50 years, n = 9) and younger (< 30 years, n = 9) groups, the baroreflex potentiation related to slow breathing was clearcut and significant for both the depressor (+46 and +24% older and younger volunteers; both P< 0.01) and the bradycardic (+130 and +73% older and younger volunteers; both P< 0.01) responses. When the assessment was made by computing the cross-spectral α index, a marked potentiation related to slow breathing was observed in younger volunteers (+99%; P< 0.01), whereas in older volunteers only a trend to an enhancement (by 32%; P< 0.055) was observed.
Slow controlled breathing is associated with potentiation of both the depressor and the cardio-inhibitory components of the arterial baroreflex, the potentiation being largely similar regardless of the age of the individual.