Effects of the self-contained breathing apparatus on left-ventricular function at rest and during graded exercise Jonathan R. Mayne, Mark J. Haykowsky, Michael D. Nelson, Timothy C. Hartley, Scott J. Butcher, Richard L. Jones, and Stewart R. Petersen Abstract: The purpose of this study was to examine the effects of the self-contained breathing apparatus (SCBA) on left- ventricular (LV) function at rest and during mild- to moderate-intensity exercise, using 2-dimensional echocardiography. Twenty-three healthy male volunteers exercised on a stair-climber at work rates equivalent to 50%, 60%, 70%, and 80% of peak oxygen consumption. Esophageal pressure LV diastolic and systolic cavity areas, and myocardial areas were ac- quired during the final minute of each stage of exercise. As expected, the esophageal pressure response during SCBA breathing revealed significantly lower (more negative) inspiratory pressures and higher (more positive) expiratory pressures and, consequently, higher pressure swings, than free breathing (FB). End-diastolic cavity area (EDCA) and end-systolic cavity area (ESCA) were lower with the SCBA than with FB. LV contractility was higher (p < 0.05) with the SCBA, which can partially be explained by decreases in end-systolic wall stress. Therefore, the SCBA was found to decrease LV preload during moderate-intensity exercise, but did not negatively affect stroke area because of a similar reduction in ESCA. Key words: intrathoracic pressure, left-ventricular function, graded exercise, self-contained breathing apparatus. Re ´sume ´: Cette e ´tude se propose d’analyser au moyen de l’e ´chocardiographie bidimensionnelle les effets d’un appareil respiratoire autonome (SCBA) sur la fonction du ventricule gauche (LV) au repos et au cours d’un exercice physique d’in- tensite ´ le ´ge `re a ` mode ´re ´e. Vingt-trois hommes participent volontairement a ` une se ´ance d’exercice sur un simulateur d’es- calier a ` une intensite ´ correspondant a ` 50 %, 60 %, 70 % et 80 % du consommation d’oxyge `ne de pointe. Durant la dernie `re minute de chaque stade d’effort, on mesure la pression œsophagienne, le volume du myocarde et du LV au cours de la diastole et de la systole. Selon toute attente, la pression œsophagienne est significativement plus faible (plus ne ´ga- tive) durant l’inspiration et plus forte (plus positive) durant l’expiration dans le SCBA; en d’autres mots, les e ´carts de pres- sion sont nettement plus importants comparativement a ` la respiration libre (FB). Comparativement a ` la FB, le volume du LV a ` la fin de la diastole (EDCA) et celui a ` la fin de la systole (ESCA) est plus petit avec le SCBA. Avec le SCBA, la contractilite ´ du ventricule gauche est supe ´rieure (p < 0,05), ce qui peut e ˆtre explique ´ en partie par la diminution de la ten- sion te ´le ´diastolique de la paroi. En conse ´quence, le SCBA diminue la pre ´charge du LV au cours d’un exercice physique d’intensite ´ mode ´re ´e, mais ne modifie pas ne ´gativement la surface d’e ´jection (SA), et ce, a ` cause de la diminution sem- blable du ESCA. Mots-cle ´s : pression intrathoracique, fonction du ventricule gauche, exercice d’intensite ´ progressive, appareil respiratoire autonome. [Traduit par la Re ´daction] Introduction Firefighters wear self-contained breathing apparatus (SCBA) for protection from hazardous airborne pollutants. However, studies from our laboratory (Eves et al. 2005; Dreger et al. 2006) have shown that the Scott 4.5 SCBA re- duces maximal aerobic power ( _ V O 2 max ). Most of the reduc- tion in _ V O 2 max and work capacity has been attributed to attenuated peak ventilation, secondary to a higher expiratory breathing resistance (Eves et al. 2005). The higher expira- tory resistance leads to increases in the work of breathing with the SCBA during submaximal exercise, when ventila- tion exceeds approximately 80 Lmin –1 (Butcher et al. 2006, 2007). Expiratory time has also been shown to lengthen dur- ing strenuous submaximal and maximal exercise with the SCBA (Eves et al. 2003, 2005; Butcher et al. 2007). Received 10 October 2008. Accepted 10 February 2009. Published on the NRC Research Press Web site at apnm.nrc.ca on 16 July 2009. J.R. Mayne, M.D. Nelson, T.C. Hartley, and S.R. Petersen. 1 Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada. M.J. Haykowsky. Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2R7, Canada; Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB T6G 2G4, Canada. S.J. Butcher. School of Physical Therapy, University of Saskatchewan, Saskatoon, SK S7N 0W3, Canada. R.L. Jones. Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2R7, Canada. 1 Corresponding author (e-mail: stewart.petersen@ualberta.ca). 625 Appl. Physiol. Nutr. Metab. 34: 625–631 (2009) doi:10.1139/H09-029 Published by NRC Research Press Appl. Physiol. Nutr. Metab. Downloaded from www.nrcresearchpress.com by 142.158.254.202 on 02/27/13 For personal use only.