title: Effects of cigarette smoking on tissue gas exchange during hyperbaric exposures.
abstract: OBJECTIVE
  In this study we investigate whether differences exist in human skeletal muscle (MM) and subcutaneous (SC) tissue gas tensions between chronic cigarette smokers and non-smokers measured under room air and hyperbaric conditions.
  
  
  METHODS
  Gas tensions in resting MM and SC tissues were recorded using a mass spectrometer at four-minute intervals during two and one-half to three-hour period in smokers and non-smokers during normobaric, normoxic (room air) and hyperbaric conditions. Two hyperbaric oxygen (HBO2) protocols were utilized: Protocol A employed the continuous breathing of oxygen (O2) at 2 ATA, a typical monoplace hyperbaric chamber treatment, while Protocol B utilized intermittent air breaks between O2 breathing periods at 2 ATA representative of a multiplace hyperbaric chamber treatment.
  
  
  RESULTS
  All tissue gas tensions changed significantly (repeated measures of variance, p=0.00001) with time as pressures and gas mixtures breathed were altered. Significant Individual Step Analysis (ISA) differences occurred with unloading of nitrogen (N2) from the muscle compartment in both protocols (T-test and Wilcoxon Rank Sum). The interaction of grouping variable and time revealed significant differences between smokers and non-smokers in unloading MM N2 in both protocols: Protocol A (p=0.02) and in Protocol B (p=0.022). Carbon dioxide (CO2) levels in both protocols decreased significantly with time when exposed to HBO2 while increasing when breathing air at 2 ATA.
  
  
  CONCLUSIONS
  This study demonstrates: 1) Smokers release MM N2 more slowly than nonsmokers during hyperbaric oxygen exposures regardless of the treatment protocol used; 2) There were no significant differences in O2 loading of MM and SC tissues during HBO2 exposures between smokers and nonsmokers; 3) The CO2 levels in both protocols decrease with time when exposed to HBO2 while increasing with breathing air at 2 ATA; 4) The known vasoconstriction effect in subcutaneous tissue from nicotine lasts less than one hour with the topical adiabatic heating increasing the O2 loading specifically in the SC tissues of smokers; 5) Wounds heal more slowly due to the chronically injured endothelium from carbon monoxide, hydrogen cyanide, and other toxic products in smoke rather than from the transient elevations of nicotine.
authors.affiliation: Department of Hyperbaric Medicine, Long Beach Memorial Medical Center, Long Beach, California, University of California Irvine, School of Medicine, Irvine, California, USA. gbabehart@hotmail.com
authors.forename: George B
authors.initials: GB
authors.lastname: Hart
authors.forename: Michael B
authors.initials: MB
authors.lastname: Strauss
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism; D002248:Carbon Monoxide / Q000378:metabolism; D002985:Clinical Protocols; D004242:Diving / Q000502:physiology; D005260:Female; D006801:Humans; D006931:Hyperbaric Oxygenation / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D012907:Smoking / Q000009:adverse effects / Q000378:metabolism*; D018709:Statistics, Nonparametric; D050151:Subcutaneous Fat / Q000378:metabolism*; D013997:Time Factors
chemical_list: D018722:Nicotinic Agonists; D002245:Carbon Dioxide; D009538:Nicotine; D002248:Carbon Monoxide; D009584:Nitrogen; D010100:Oxygen