Schlader, Zachary J.

We tested the hypothesis that ventilation (VE) and the hypoxic ventilatory response (HVR) during hyperthermia would be attenuated when carotid body chemosensitivity is blunted by an IV infusion of dopamine (2 µg/kg/min) vs. IV saline. We studied 9 subjects (1 woman, 32 ± 2 years, 25.7 ± 0.7 kg/m2) over two randomized dopamine and saline study visits. We measured VE and HVR (3 minutes at: room air, 16% O2, and 10% O2) at baseline and during normothermia (NORMInf) and hyperthermia (HYPInf) (core temperature 1.2‐1.5°C above baseline) infusion conditions. VE increased during HYPInf vs. NORMInf during dopamine (8.2 ± 0.3 vs. 10.2 ± 1.1 L/min; P = 0.04) and saline (8.9 ± 0.3 vs. 9.7 ± 0.5 L/min; P = 0.04) with no difference between conditions (P = 0.95). HVR during saline increased from baseline (0.30 ± 0.1 L/min/%SaO2; P < 0.01) and NORMInf (0.42 ± 0.1 L/min/%SaO2; P = 0.02) to HYPInf (0.77 ± 0.2 L/min/%SaO2). HVR did not change throughout the dopmaine visit (baseline = 0.38 ± 0.1; NORMInf = 0.27 ± 0.1; HYPInf 0.42 ± 0.1 L/min/%SaO2; P > 0.46). Dopamine HVR was lower than saline during HYPInf (P < 0.01). These data indicate that carotid body chemosensitivity to hypoxia is augmented during hyperthermia and that low dose dopamine was unable to lower normoxic VE during hyperthermia. Grant Funding Source : Supported by NIH R01DK090541 and RO1HL61388

We tested the hypothesis that administering low‐dose dopamine (2 mcg/kg/min) to desensitize the carotid body chemoreceptors would alter metrics of heart rate variability (HRV). Electrocardiogram (ECG) recordings were obtained from 18 healthy adults (age = 31 ± 2 years; BMI = 24.6 ± 0.6 kg/m 2 ) during two randomized study days where they received an IV infusion of saline (S) or dopamine (DA). HRV was analyzed during five minute segments at baseline and during infusions of S and DA. Time‐domain analysis of the root mean square of the successive differences (RMSSD) along with spectral domain analysis of low (LF) and high frequency (HF) were obtained. There were no differences (P > 0.05) in respiration rate or blood pressure at any time point. Heart rate increased from baseline during DA (60 ± 2 vs. 63 ± 2 bpm; P < 0.01) and during infusion it was greater in DA vs. S (63 ± 2 vs. 58 ± 2 bpm; P < 0.01). RMSSD decreased from baseline to infusion during DA (68.2 ± 7.6 vs. 51.6 ± 6.0 ms; P < 0.01) and during infusion it was lower in DA vs. S (78.3 ± 10.3 vs. 51.6 ± 6.0 ms; P < 0.01). HF was reduced during DA vs. baseline (1733± 301 vs. 870 ± 171 ms 2 ; P < 0.01), and during infusion DA was also lower than S (1936 ± 471 vs. 870 ± 171 ms 2 ; P = 0.02). There were no changes (P > 0.05) in LF, LF/HF or normalized HF and LF values. These data indicate that during resting conditions the carotid body chemoreceptors likely modulate parasympathetic components of HRV in healthy adults. Grant Funding Source : Supported by NIH R01DK090541 and RO1HL61388

Environmental stressors, such as heat or altitude, elicit dissimilar physiological adaptations to endurance training programs. Whether these differences (i.e., increased hemoglobin mass vs plasma volume) differentially influence performance is debated. We review data in support of our novel hypothesis, which proposes altitude as the preferred environmental training stimulus for elite endurance athletes preparing to compete in temperate, sea-level climates (5°C–18°C).