Combined influence of inspiratory loading and locomotor subsystolic cuff inflation on cardiovascular responses during submaximal exercise

Abstract

It is unknown if simultaneous stimulation of the respiratory and locomotor muscle afferents via inspiratory loading (IL) and locomotor subsystolic cuff inflation (CUFF) influences the cardiovascular responses during exercise. We hypothesized that combined IL and CUFF (IL + CUFF) will result in greater increases in blood pressure (MAP) and systemic vascular resistance (SVR) than IL and CUFF alone during exercise. Eight adults (6 males/2 females) were enrolled and performed four 10-min bouts of constant-load cycling eliciting 40% maximal oxygen uptake on a single day. For each exercise bout, the first 5 min consisted of spontaneous breathing. The second 5 min consisted of voluntary hyperventilation (i.e., breathing frequency of 40 breaths/min) with IL (30% maximum inspiratory pressure), CUFF (80 mmHg), IL + CUFF, or no intervention (CTL) in randomized order. During exercise, cardiac output and MAP were determined via open-circuit acetylene wash-in and manual sphygmomanometry, respectively, and SVR was calculated. Across CTL, IL, CUFF, and IL + CUFF, MAP was greater with each condition (CTL: 97 ± 14; IL: 106 ± 13; CUFF: 114 ± 14; IL + CUFF: 119 ± 15 mmHg, all P < 0.02). Furthermore, SVR was greater with IL + CUFF compared with IL, CUFF, and CTL (CTL: 6.6 ± 1.1; IL: 7.5 ± 1.4; CUFF: 7.5 ± 1.3; IL + CUFF: 8.2 ± 1.4 mmHg·L^-1·min^-1, all P < 0.02). Cardiac output was not different across conditions (CTL: 15.2 ± 3.8; IL: 14.8 ± 3.7; CUFF: 15.6 ± 3.5; IL + CUFF: 14.7 ± 4.3 L/min, all P > 0.05). These data demonstrate that simultaneous stimulation of respiratory and locomotor muscle afferent feedback results in additive MAP and SVR responses than IL and CUFF alone during submaximal exercise. These findings have important clinical implications for populations with exaggerated locomotor and respiratory muscle reflex feedbacks.NEW & NOTEWORTHY Reflexes arising from the respiratory and locomotor muscles influence cardiovascular regulation during exercise. However, it is unclear how the respiratory and locomotor muscle reflexes interact when simultaneously stimulated. Herein, we demonstrate that stimulation of the respiratory and locomotor muscle reflexes yielded additive cardiovascular responses during submaximal exercise.

Keywords: blood pressure; cardiac output; exercise pressor reflex; respiratory muscle metaboreflex; venous distention.

Fig. 1.

Blood pressure (MAP) response with simultaneous inspiratory loading (IL) and subsystolic cuff inflation (CUFF) during submaximal exercise. Mean and individual MAP during submaximal exercise with no intervention (CTL), IL, CUFF, and IL + CUFF. Significant differences were present in MAP across all conditions (all P < 0.02). ^αSignificantly different from previous condition.

Fig. 2.

Cardiac output (Q) response with simultaneous inspiratory loading (IL) and subsystolic cuff inflation (CUFF) during submaximal exercise. Mean and individual Q (A and B), stroke volume (C and D), and heart rate (E and F) during submaximal exercise with no intervention (CTL), IL, CUFF, and IL + CUFF. There were no differences in Q across conditions (all P > 0.05). Stroke volume was lower during IL and IL + CUFF compared with CTL (both P < 0.01). Lastly, heart rate was greater during the IL, CUFF, and IL + CUFF compared with CTL (both P < 0.02). *Significantly different from CTL.

Fig. 3.

Systemic vascular resistance response with simultaneous inspiratory loading (IL) and subsystolic cuff inflation (CUFF) during submaximal exercise. Mean and individual systemic vascular resistance (SVR) during submaximal exercise with no intervention (CTL), IL, CUFF, and IL + CUFF. SVR was higher with IL, CUFF, and IL + CUFF than CTL (all P < 0.01). Furthermore, SVR was greater with IL + CUFF compared with IL and CUFF (all P < 0.02). Significantly different from CTL (*) and IL + CUFF (†).

Fig. 4.

Changes in blood pressure (MAP), cardiac output (Q), and systemic vascular resistance (SVR) from control (CTL) during submaximal exercise. Mean and individual changes in MAP (A and B), Q (C and D), and SVR (E and F) with inspiratory loading (IL), subsystolic cuff inflation (CUFF), and IL + CUFF from CTL. The change in MAP from CTL was significantly different across IL, CUFF, and IL + CUFF (all P < 0.03). The change in SVR from CTL was higher with IL + CUFF compared with IL and CUFF (both P < 0.05). Significantly different from IL + CUFF (†) and from previous condition (α).