Global REACH 2018: The carotid artery diameter response to the cold pressor test is governed by arterial blood pressure during normoxic but not hypoxic conditions in healthy lowlanders and Andean highlanders

Abstract

The impact of oxygen on the circulatory responses to a cold pressor test (CPT) in lowlanders and Andean highlanders remains unknown. Our hypotheses were as follows: (i) in lowlanders, acute normobaric and hypobaric hypoxia would attenuate the common carotid artery (CCA) diameter response to the CPT compared with normobaric normoxia; (ii) Andean highlanders would exhibit a greater CCA diameter response compared with lowlanders; and (iii) a positive relationship between CCA diameter and blood pressure in response to the CPT would be present in both lowlanders and highlanders. Healthy lowlanders (n = 13) and Andean highlanders (n = 8) were recruited and conducted an isocapnic CPT, which consisted of a 3 min foot immersion into water at 0-1 • C. Blood pressure (finger photoplethysmography) and CCA diameter and blood flow (Duplex ultrasound) were recorded continuously. The CPT was conducted in lowlanders at sea level in isocapnic normoxic and hypoxic conditions and after 10 days of acclimatization to 4300 m (Cerro de Pasco, Peru) in hypoxic and hyperoxic conditions. Andean highlanders were tested at rest at high altitude. The main findings were as follows: (i) in lowlanders, normobaric but not hypobaric hypoxia elevated CCA reactivity to the CPT; (ii) no differences in response to the CPT were observed between lowlanders and highlanders; and (iii) although hypobaric hypoxaemia reduced the relationship between CCA diameter and blood pressure compared with normobaric normoxia (P = 0.132), hypobaric hyperoxia improved this

Sex differences in the vascular response to sympathetic activation during acute hypoxaemia

“…(2) the systemic vasoconstrictor response to sympathetic activation is augmented during hypoxaemia in men, but not in women; and (3) the local forearm vasoconstrictor response to sympathetic activation is attenuated during hypoxaemia in women only. Our results in men confirm previous findings in cohorts of predominantly male participants (Dinenno et al, 2003;Tan et al, 2013;Tymko et al, 2020;Rowell & Blackmon, 1986), and we now extend them to highlight sex-related differences in neurovascular control during systemic hypoxia.…”

“…The CPT is a well-established sympathoexcitatory stimulus used to assess α-adrenergic receptor-mediated vasoconstriction in humans (Dinenno et al, 2001;Frank & Raja, 1994;Kooijman et al, 2009). Similar to previous studies, including those utilizing the CPT, we found the vascular response to sympathetic activation was maintained (Figure 2a; Dinenno et al, 2003;Tymko et al, 2020;Roweel & Blackmon, 1986) or even enhanced (Figure 1a; Tan et al, 2013) in healthy young men during systemic hypoxia. Although the majority of prior work in humans has focused on the skeletal muscle vasculature, vascular responsiveness to sympathetic activation during systemic hypoxia may differ by vascular bed (Gonzales et al, 2008).…”