Vagal blockade suppresses the phase I heart rate response but not the phase I cardiac output response at exercise onset in humans

Figures

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  Fig. 1. Difference (Δ) in heart rate, cardiac output, stroke volume and oxygen consumption between rest and exercise steady state in supine and upright position and for control situation and with atropine (n = 9). \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2 oxygen consumption, CO cardiac output, HR heart rate, SV stroke volume, *p < 0.05 vs. supine position; #p < 0.05 vs. control

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  Fig. 2. Calculated arterial-venous O2 difference between rest and exercise steady state in supine and upright position and for control situation and with atropine. CaO2–C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{v }$$\end{document}v¯O2 arterial-venous O2 difference; *p < 0.05 vs. rest

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  Fig. 3. Individual examples of the time course of heart rate and cardiac output in supine and upright position and for control situation and with atropine. Single beat data (grey trace) and corresponding fitting function (black line) are reported. A–D heart rate (min−1); E–H: cardiac output (L min−1). Conditions: A, E control supine; B, F control upright; C, G atropine supine; D, H atropine upright. All traces were fitted by the double exponential model (sum of two exponentials). However, fitting of the traces reported in C (atropine supine, heart rate) and D (atropine upright, heart rate) yielded phase I amplitude equal to zero: thus, they were fitted as monoexponential functions, due to the absence of phase I, as detailed in the method section

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  Fig. 4. Heart rate kinetics between rest and exercise steady state in supine and upright position and for control situation and with atropine. HR heart rate, A amplitude, τ time constant. The subscripts 1 and 2 refer to the φ1 and the φ2 of the bi-exponential model; (n): number of subjects on which τ1 was computed; *p < 0.05 vs. supine position; #p < 0.05 vs. control

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  Fig. 5. Cardiac output kinetics between rest and exercise steady state in supine and upright position and for control situation and with atropine. CO cardiac output, A amplitude, τ time constant. The subscripts 1 and 2 refer to the φ1 and the φ2 of the bi-exponential model; (n): number of subjects on which τ1 was computed. *p < 0.05 vs. supine position; #p < 0.05 vs. control

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  Fig.6. Oxygen consumption kinetics at rest and exercise steady state in supine and upright position and for control situation and with atropine. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2 oxygen uptake, A amplitude, τ: time constant. The subscripts 1 and 2 refer to the φ1 and the φ2 of the bi-exponential model; (n): number of subjects on which τ1 was computed. *p < 0.05 vs. supine position