Heart rate and blood pressure time courses during prolonged dry apnoea in breath-hold divers

Abstract

To define the dynamics of cardiovascular adjustments to apnoea, beat-to-beat heart rate (HR) and blood pressure and arterial oxygen saturation (SaO(2)) were recorded during prolonged breath-holding in air in 20 divers. Apnoea had a mean duration of 210 +/- 70 s. In all subjects, HR attained a value 14 beats min(-1) lower than control within the initial 30 s (phase I). HR did not change for the following 2-2.5 min (phase II). Then, nine subjects interrupted the apnoea (group A), whereas 11 subjects (group B) could prolong the breath-holding for about 100 s, during which HR continuously decreased (phase III). In both groups, mean blood pressure was 8 mmHg above control at the end of phase I; it then further increased by additional 12 mmHg at the end of the apnoea. In both groups, SaO(2) did not change in the initial 100-140 s of apnoea; then, it decreased to 95% at the end of phase II. In group B, SaO(2) further diminished to 84% at the end of phase III. A typical pattern of cardiovascular readjustments was identified during dry apnoea. This pattern was not compatible with a role for baroreflexes in phase I and phase II. Further readjustment in group B may imply a role for both baroreflexes and chemoreflexes. Hypothesis has been made that the end of phase II corresponds to physiological breakpoint.

Cardiovascular responses to dry resting apnoeas in elite divers while breathing pure oxygen

“…At the beginning of apnoea, the immediate response consisted of a rapid fall of SBP and DBP, as previously observed at rest (Andersson and Schagatay, 1998;Palada et al, 2007;Perini et al, 2008) and at exercise (Sivieri et al, 2015). This fall was associated with a reduction of SV, supporting the notion that the fall of SBP may be due to an acute reduction of venous return related to the act of holding the breath at elevated lung volumes (Andersson and Schagatay, 1998).…”

“…After 5 min had been allowed to achieve steady state conditions, 10 min of measurements were obtained with the subject at rest and spontaneously breathing (quiet rest). Then, the subject was asked to perform two successive maximal apnoeas, separated by a recovery interval of 2 min (Perini et al, 2008). Maximal apnoeas are defined as apnoeas prolonged to volitional exhaustion.…”

“…In recent years, changes in blood pressure, heart rate (f H ), stroke volume (SV), cardiac output (Q ) and total peripheral resistance (TPR) in response to apnoea (cardiovascular response to apnoea) were determined beat-by-beat on elite divers during apnoeas prolonged to the volitional breaking point (Costalat et al, 2013;Lemaître et al, 2008;Perini et al, 2008Perini et al, , 2010Sivieri et al, 2015). These studies described the cardiovascular response to apnoea as consisting of three distinct phases: (i) a short dynamic phase ( 1), that lasts less than 30 s, characterised by rapid changes in blood Abbreviation: DBP, diastolic blood pressure; fH, heart rate; FIO2, inspired oxygen fraction; MBP, mean blood pressure;Q , cardiac output; SaO2, arterial oxygen saturation; SBP, systolic blood pressure; SV, stroke volume; TPR, total peripheral resistance;V O2, oxygen uptake; 1, first, dynamic phase of the cardiovascular response to apnoea; 2, second, steady-state phase of the cardiovascular response to apnoea; 3, third, dynamic phase of the cardiovascular response to apnoea.pressure and f H ; (ii) a steady state phase ( 2), of about 2 min, in which the values attained by each variable at the end of 1 are maintained invariant; and (iii) a further subsequent dynamic phase ( 3), lasting about 1.5 min, characterised by a continuous decrease in f H and increase in blood pressure, until the volitional breaking point was reached.…”

“…These studies described the cardiovascular response to apnoea as consisting of three distinct phases: (i) a short dynamic phase ( 1), that lasts less than 30 s, characterised by rapid changes in blood Abbreviation: DBP, diastolic blood pressure; fH, heart rate; FIO2, inspired oxygen fraction; MBP, mean blood pressure;Q , cardiac output; SaO2, arterial oxygen saturation; SBP, systolic blood pressure; SV, stroke volume; TPR, total peripheral resistance;V O2, oxygen uptake; 1, first, dynamic phase of the cardiovascular response to apnoea; 2, second, steady-state phase of the cardiovascular response to apnoea; 3, third, dynamic phase of the cardiovascular response to apnoea.pressure and f H ; (ii) a steady state phase ( 2), of about 2 min, in which the values attained by each variable at the end of 1 are maintained invariant; and (iii) a further subsequent dynamic phase ( 3), lasting about 1.5 min, characterised by a continuous decrease in f H and increase in blood pressure, until the volitional breaking point was reached. According to Perini et al (2008Perini et al ( , 2010, the end of 2 might occur at the attainment of the physiological breaking point of apnoea (Hong et al, 1971), which is characterised by a specific alveolar PO 2 and PCO 2 composition possibly capable of inducing the first diaphragmatic contraction (Agostoni, 1963;Cross et al, 2013;Lin et al, 1974;Whitelaw et al, 1981): the higher is the alveolar PO 2 , the higher must be the concomitant PCO 2 eliciting diaphragmatic contractions, and vice versa. Ceteris paribus, the time necessary to reach that alveolar gas composition is directly proportional to the body oxygen stores at the beginning of the apnoea and inversely proportional to the body metabolic rate during apnoea.…”

“…The general hypothesis of this study is that the onset of 3 is related to the onset of diaphragmatic contractions, requiring the attainment of a specific alveolar gas composition and representing the so-called physiological breaking point of apnoea, as proposed by Perini et al (2008Perini et al ( , 2010. In the context of this hypothesis, we postulated that the three phases of the cardiovascular response to apnoea would be present both at FIO 2 = 1 and at FIO 2 = 0.21, but the duration of 2 and 3 would be longer in the former than in the latter condition.…”