Relationships between the extent of apnea-induced bradycardia and the vascular response in the arm and leg during dynamic two-legged knee extension exercise

Abstract

Nishiyasu T, Tsukamoto R, Kawai K, Hayashi K, Koga S, Ichinose M. Relationships between the extent of apnea-induced bradycardia and the vascular response in the arm and leg during dynamic two-legged knee extension exercise. Am J Physiol Heart Circ Physiol 302: H864 -H871, 2012. First published December 9, 2011; doi:10.1152/ajpheart.00413.2011.-Our aim was to test the hypothesis that apnea-induced hemodynamic responses during dynamic exercise in humans differ between those who show strong bradycardia and those who show only mild bradycardia. After apneainduced changes in heart rate (HR) were evaluated during dynamic exercise, 23 healthy subjects were selected and divided into a large response group (L group; n ϭ 11) and a small response group (S group; n ϭ 12). While subjects performed a two-legged dynamic knee extension exercise at a work load that increased HR by 30 beats/min, apnea-induced changes in HR, cardiac output (CO), mean arterial pressure (MAP), arterial O2 saturation (SaO 2 ), forearm blood flow (FBF), and leg blood flow (LBF) were measured. During apnea, HR in the L group (54 Ϯ 2 beats/min) was lower than in the S group (92 Ϯ 3 beats/min, P Ͻ 0.05). CO, SaO 2 , FBF, LBF, forearm vascular conductance (FVC), leg vascular conductance (LVC), and total vascular conductance (TVC) were all reduced, and MAP was increased in both groups, although the changes in CO, TVC, LBF, LVC, and MAP were larger in the L group than in the S group (P Ͻ 0.05). Moreover, there were significant positive linear relationships between the reduction in HR and the reductions in TVC, LVC, and FVC. We conclude that individuals who show greater apnea-induced bradycardia during exercise also show greater vasoconstriction in both active and inactive muscle regions. mean arterial pressure; femoral blood flow; breath hold LARGE CARDIOVASCULAR RESPONSES occur during breath-hold diving in both animals and humans (10,12,14,19,28,36). The response is characterized by bradycardia and vasoconstriction related to the so-called "diving reflex" (1,8,10,20,24,36), and it has been proposed that the function of these changes is primarily to preserve an adequate O 2 supply to vital organs (1,4,15,18,19,24). Some diving animals, such as seals, show remarkable bradycardia during voluntary diving (36). In humans, the bradycardic response seen during apnea or diving is smaller than in diving animals and varies a great deal from individual to individual (5,21,24,31,32).Acute apnea-induced bradycardia is observed in humans during exercise on land (3,4,6,7,22,25,26,27,30,33). Bjertnaes et al. (7) reported that during exercise, the decrease in cardiac output (CO) induced by apnea was nearly paralleled by a reduction in heart rate (HR). In addition, Lindholm et al. (27) reported that the extent of the bradycardia induced by apnea during exercise had a significant negative relationship with the reduction in arterial blood O 2 saturation (Sa O 2 ) and suggested that the reduction in CO during apnea could conserve O 2 in arterial blood during apnea in exercisin...

Influence of Apnea-induced Hypoxia on Catecholamine Release and Cardiovascular Dynamics

“…Greater bradycardia was accompanied by greater vascular responses. Furthermore, they found a linear relationship between HR reduction, an increase in vasoconstriction, and thus an increase in MAP during breath-hold [34]. We only found a slight correlation between increase of systolic blood pressure and heart-rate reduction during dry apnea.…”

“…We saw a drop of HR (i. e., decrease of HR ≥ 10 bpm) in only 5 of 11 divers. In a previous study Nishiyasu et al [34] compared divers developing strong apnea-induced bradycardia with those who show only mild bradycardia. Greater bradycardia was accompanied by greater vascular responses.…”

Evaluation of near-infrared spectroscopy under apnea-dependent hypoxia in humans

“…A raised total peripheral resistance (TPR) and an increased mean arterial pressure (MAP) during apnea has been reported in case of divers [28][29][30][31][32]. We could also measure significantly elevated MAP in the course of apnea in a subset of measurements.…”

“…In a previous study by Nishiyasu et al [28] the authors describe two groups with different physiological reactions following apnea. Subjects of the first group developed lower heart rates (\65 beats/min) and exhibited greater changes in MAP and TPR compared to a second group maintaining a minimum heart rate above 75 beats/min.…”

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“…Occlusion cuff pressures were measured using a pressure transducer mounted on the cuff. We measured cardiac output (CO) using Doppler ultrasound as previously described (28,30). Briefly, a Doppler ultrasound system (HDI 5000; ATL Ultrasound), equipped with a handheld transducer probe (model D2 CW) with an operating frequency of 2 MHz, was used to continuously measure ascending aortic blood velocity.…”