A group of Italian researchers reports in the November issue of the Journal of Applied Physiology that while breathing a low-density mixture of 79% helium and 21% oxygen (called heliox), the length of time that 12 COPD patients could do real exercise was 9 minutes, versus only 4.2 minutes for 12 patients breathing regular air (79% nitrogen/21% oxygen). And the exercise involved wasn't trivial: The subjects cycled "until exhaustion" at a rate of 50 rpm at 80% of their maximal rate measured several days earlier while on air.
COPD: 4th leading cause of death in world and U.S., and rising
The World Health Organization estimates that chronic obstructive pulmonary disease (COPD, defined as emphysema and chronic bronchitis) as a single cause of death around the world shares fourth place with HIV/AIDS, following coronary heart disease, cerebrovascular disease and acute respiratory infection. WHO estimates that 2,740,000 people died of COPD worldwide in 2000; cigarette smoking is blamed for about 85% of cases.
According to the National Heart, Lung, and Blood Institute (NHLBI), COPD is the fourth leading cause of death in the U.S. and is projected to rise to third place for both men and women by the year 2020. NHLBI says 12.1 million Americans 25 and older were diagnosed with COPD in 2001. Estimated cost of COPD in 2002 was $32.1 billion, of which $18 billion were direct costs.
COPD is characterized by shortness of breath (dyspnea) and exercise intolerance. Among severely affected patients, especially those with emphysema, the inability to exercise or even to move small distances is mostly due to limits on "breathing out" because of limited expiratory flow, and early onset of dyspnea.
Heliox appears to positively change multitude of lung mechanics
In the current study, the more than doubling in the time COPD patients could exercise "was associated with a significant reduction in lung dynamic hyperinflation (DH) at isotime (Iso; when the patients stopped exercising during regular air breathing), as reflected by the increase in inspiratory capacity (IC) to 1.97 from 1.77 liters and a decrease in dyspnea" scoring to 6 from 8.
The researchers said that "heliox induced a state of relative hyperventilation as reflected by the increase in minute ventilation" to 38.3 versus 35.5 liters, and minute ventilation over carbon dioxide output to 36.3 versus 33.9 at peak exercise, and by the reduction in arterial partial pressure of carbon dioxide at Iso to 44 from 48 and at peak exercise to 46 from 48.
The study, "Effect of heliox on lung dynamic hyperinflation, dyspnea, and exercise endurance capacity in COPD patients," was conducted by Paolo Palange, Gabriele Valli, Paolo Onorati, Rosa Antonucci, Patrizia Paoletti, Alessia Rosato, Felice Manfredi, and Pietro Serra from Dipartmento di Medicina Clinica, Servizio di Fisiopatologia Respiratoria, Università "La Sapienza," Rome, Italy.
Palange et al. says the "most likely explanation for our finding is that heliox improved maximal expiratory flow and maximal ventilatory capacity, as reflected by the increase in resting forced expiratory volume and by the increase in tidal volume, mean expiratory flow, and minute ventilation at peak exercise. Importantly, the improvement in maximal expiratory flow determined a significant reduction in lung dynamic hyperinflation and dyspnea, as reflected by the significant increase in inspiratory capacity (IC), inspiratory reserve volume and IC/minute ventilation, and decrease in dyspnea at Iso.
"All of these positive changes in lung mechanics allowed the patients to markedly improve exercise endurance time," they note.
And finally, "it is likely that the exercise protocol used, capable of inducing high levels of ventilation relative to subject's maximal ventilation for a prolonged period of time, has amplified the effect of heliox breathing in reducing turbulent airway resistances," the authors say. In a related observation, they believe that "the high-intensity constant work rate test utilized allowed us to clearly detect the beneficial effect of small changes in lung mechanics induced by heliox breathing on exercise capacity."
The authors conclude that "heliox breathing, by reducing airflow limitations, lung dynamic hyperinflation and dyspnea sensation, is capable of improving high-intensity exercise endurance capacity in moderate to severe COPD patients." However, they note that "further studies are needed to verify the potential role of heliox supplementation during exercise rehabilitation programs in COPD patients."
The study, "Effect of heliox on lung dynamic hyperinflation, dyspnea, and exercise endurance capacity in COPD patients," by Palange et al. appears in the November issue of the Journal of Applied Physiology, published by the American Physiological Society.
Editor's note: A copy of the research paper by Palange et al. is available to the media. Members of the media are encouraged to obtain an electronic version and to interview members of the research team.
To do so, please contact Mayer Resnick at the American Physiological Society, 301-634-7209, cell 301-332-4402 or email@example.com.
The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has more than 10,000 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually.
APS provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In May, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring (PAESMEM).