Tachypnea and hypocapnia are induced by ‘buffeting’ in vehicles

Abstract

Normal physiological responses to vehicular buffeting were studied during a 5 minute mild 'off road' exposure in a motion simulator. The ride provoked an initial increase in heart rate and blood pressure and a significant hypocapnia of P(ET) CO(2) 34 mm Hg caused by tachypnea, which took 5 minutes to recover. Motion induced hypocapnia could be a source of distress for vulnerable subjects and patients when travelling.

Respiratory vulnerability to vehicle buffeting

“…No significant changes in blood pressure in response to buffeting were observed in our earlier, normative studies [6,7]. These also showed a slightly but significant increase in heart rate for 2-3 min about the time of onset of motion from an overall mean R-R interval of 0.8 s, SD 0.05-0.75 s, thereafter returning to baseline levels throughout motion (normative data from Green et al [6]).…”

“…The methods have been described previously in this journal [6,7]. In brief, subjects sat in a flight simulator restrained by a 4 point harness.…”

“…Normative data was established in recent studies using the same equipment and protocol [6,7] involving subjects in the age range 21-56 years. The subjects providing normative data completed extensive medical questionnaires which probed all relevant aspects of cardiovascular, respiratory, neurological and otological function and use of prescribed or social drugs.…”

“…The normal response to mild buffeting, as would be experienced in a jerky bus ride or an emergency ambulance, is a stereotypical elevation of breathing frequency which persists throughout motion [6,7]. A normal depth of breathing is maintained during the first 3-5 min of motion so that the subjects 'overbreathe' lowering PET CO 2 by a mean of 2-3 mmHg with certain individuals dropping to 34 mmHg PET CO 2 .…”

“…Although the mechanical and ventilatory effects of mild buffeting on normal subjects are of little consequence, this study explores the possibility that vulnerable subjects who either fail to reinforce the trunk or to adapt depth of breathing to counter hypocapnia, might suffer more serious consequences [6].…”