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. 2012 Apr 23;590(Pt 14):3277–3290. doi: 10.1113/jphysiol.2012.230425

Table 1.

Steady-state cardiorespiratory and cerebrovascular changes from normocapnia to hypocapnia and two levels of hypercapnia

Hypercapnia
Hypocapnia Normocapnia (baseline) 3% CO2 6% CO2
Cardiorespiratory
 Inline graphic (mmHg) 21.1 ± 3.1* 38.9 ± 2.4 46.1 ± 3.1* 53.9 ± 2.8*
 Estimated Inline graphic (mmHg) 21.0 ± 2.8* 36.8 ± 2.1 43.6 ± 2.7* 50.0 ± 2.5*
 Inline graphic (l min−1) 45.0 ± 5.9* 9.4 ± 1.2 16.2 ± 2.8* 24.9 ± 4.7*
 HR (beats min−1) 86 ± 15* 63 ± 8 68 ± 11 72 ± 13*
 MAP (mmHg) 89 ± 6 87 ± 9 90 ± 8 94 ± 9†
 Cardiac output (%) 139 ± 21* 100 110 ± 9† 120 ± 14*
Cerebrovascular
 ICA blood flow (ml min−1) 160±33* 235±47 283±53* 386±112*
 Dmean (cm) 0.45±0.06 0.45±0.06 0.46±0.05 0.46±0.05
 Vmean (cm s−1) 17.7±4.4* 24.7±4.8 28.9±5.7* 38.1±9.4*
 VA blood flow (ml min−1) 81±16* 112±27 126±34† 153±45*
 Dmean (cm) 0.34±0.04 0.35±0.04 0.35±0.03 0.36±0.04
 Vmean (cm s−1) 15.8±4.7* 20.4±5.6 22.0±5.3 25.9±6.6*
 ECA blood flow (ml min−1) 102±37 113±42 113±43 127±55
 Dmean (cm) 0.37±0.07 0.36±0.07 0.37±0.07 0.37±0.07
 Vmean (cm s−1) 15.8±4.4† 18.4±4.9 17.6±4.7 19.3±5.5
 MCA Vmean (cm s−1) 29.4±7.2* 57.4±14.0 65.7±16.2* 85.2±15.2*
 BA Vmean (cm s−1) 22.8±6.7* 32.0±7.3 37.1±5.5† 46.3±7.7*

Values are mean ± SD Inline graphic, end-tidal CO2; Estimated Inline graphic, regression equation using end-tidal CO2 to estimated Inline graphic; Inline graphic, minute ventilation; HR, heart rate; MAP, mean arterial pressure; ICA, internal carotid artery; VA, vertebral artery; ECA, external carotid artery; Dmean, mean vessel diameter; Vmean, mean blood flow velocity. †Different from normocapnia (P < 0.05); *different from normocapnia (P < 0.01).