Influence of inspiratory threshold load on cardiovascular responses to controlled breathing at 0.1 Hz

Abstract

Slow, deep breathing is being used as a self‐management intervention for various health conditions including pain and hypertension. Stimulation of the arterial baroreceptors and increased vagal modulation are among the proposed mechanisms for the therapeutic effects of slow, deep breathing. We investigated whether adding inspiratory threshold load can enhance the cardiovascular responses to controlled breathing at the frequency of 0.1 Hz, a common form of slow, deep breathing. Healthy volunteers (N = 29) performed controlled breathing at 0.1 Hz (6 breaths/minute) without load and with inspiratory threshold loads of 5 cmH2O and 10 cmH2O. Respiratory airflow, heart rate, and blood pressure were continuously recorded. The amplitude of the systolic blood pressure variation during respiratory cycles increased with increasing loads. Respiratory sinus arrhythmia was higher during controlled breathing at 0.1 Hz with the load of 10 cmH2O compared to without load. Baroreflex sensitivity was not affected by loads. The effect of loads on respiratory sinus arrhythmia was mediated by increasing the amplitude of systolic blood pressure variation during respiratory cycles. These results suggest that applying small inspiratory threshold loads during controlled breathing at 0.1 Hz increases cardiac vagal modulation by this breathing exercise. This effect seems to be mediated by stronger stimulation of the arterial baroreceptors because of larger systolic blood pressure swings along the respiratory cycle. The potential benefit of long‐term practice of controlled breathing at 0.1 Hz with inspiratory threshold loads on baroreflex function and cardiac vagal control needs to be investigated, particularly in pain and hypertension patients.

Psychophysiological responses to various slow, deep breathing techniques

“…We recently showed that using an ITL during SDB further increases blood pressure variability at the frequency of breathing followed by increased respiratory sinus arrhythmia (RSA). Although we found no further change in baroreflex sensitivity by using ITL, with the baroreflex operating within a larger range of blood pressure fluctuations, the application of ITL during SDB can enhance stimulation of the arterial (high‐pressure) baroreceptors (Gholamrezaei et al., 2019). These responses may explain the beneficial effects of loaded SDB in patients with hypertension and may also extend to pain as stimulation of the baroreceptors and autonomic modulation during SDB are proposed to have hypoalgesic effects (Jafari et al., 2017).…”

“…The flow‐independent threshold load (Threshold PEP, Respironics Inc., NJ, US) was used and set to a load of 10 cmH 2 O based on our previous study (Gholamrezaei et al., 2019). A nose clip was used to help the participant to breathe only through the mouth during loaded SDB.…”

“…Considering that participants (especially novices) may experience dyspnea during slow breathing (Allen & Friedman, 2012; Szulczewski, 2019) and particularly during loaded SDB (Gholamrezaei et al., 2019), dyspnea (phrased as “difficulty in breathing”) was measured using the modified Borg scale with scores ranging from 0 (nothing at all) to 10 (intolerable) (Borg, 1982). Emotional responses were assessed in three dimensions of arousal, valence, and dominance using the 9‐point Self‐Assessment Manikin scale.…”

“…Further, we compared the emotional impact of these SDB techniques including the dimensions arousal, valence, and dominance. This study had two priori hypotheses: (1) considering that closing one nostril increases the resistance to airflow and works as a resistive load (Pallanch et al., 1985), and based on our previous findings on loaded SDB (Gholamrezaei et al., 2019), we hypothesized that blood pressure and heart rate variability would be higher during UNB and loaded SDB versus PLB; and (2) since nasal breathing is more ecologically valid than mouth breathing in a resting state (Gilbert, 2014), we hypothesized that UNB and PLB would be associated with less arousal, more pleasantness, and more sense of control compared with loaded SDB.…”

Can Slow Deep Breathing Reduce Pain? An Experimental Study Exploring Mechanisms

“…Deeper breathing during SDB causes greater fluctuations in intrathoracic pressure, cardiac filling, and blood pressure along the respiratory cycle, which results in greater RSA. 25,26,42,48,56 The magnitude of RSA and vagal activity is further increased when breathing at one's particular "resonance frequency," which on average lies around.1 Hz, and at which resonance properties of the baroreflex system may further enhance RSA and cardiac vagal activity. 61,62 Finally, cardiac vagal activity was found to be higher when breathing with lower compared to higher inspiration/expiration ratios (eg, 3s/7s vs 7s/3s, 60 or 2s/8s vs 8s/2s 9 ), that is, when expiration is long relative to inspiration.…”