The nose also effectively conditions inspired air to near body temperature and between 98-100% relative humidity before it enters the lungs. The ability of the nose to condition ambient air in these ways serves as a protective mechanism against toxicity to the lower respiratory tract.
A New Study
The results of a new study entitled "Nasal Contribution to Breathing With Exercise: Effect of Race and Gender" have been published. The authors are William D. Bennett and Kirby L. Zeman from the Center for Environmental Medicine, Asthma and Lung Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC; and Annie M. Jarabek of the National Center for Environmental Assessment, US Environmental Protection Agency, Research Triangle Park, NC. Their findings appear in the August 2003 edition of the Journal of Applied Physiology, one of 14 scientific journals published monthly by the American Physiological Society (APS) (http://www.
A group of healthy, nonsmoking adults, age 18-31 yr, were studied, of which 11 were Caucasian (6 men/5 women) and 11 were African-American (5 men/6 women). The subjects had no history of lung disease and no recent history of acute respiratory infection or viral illness within the previous 4 weeks. A few subjects reported seasonal nasal allergies and associated rhinitis but were asymptomatic during the time of study. Forced expiratory volume and forced vital capacity were determined for each subject by spirometry.
A measure of each subject's predicted maximum exercise capacity on a cycle ergometer was determined. While being monitored by an ECG, subjects performed graded submaximal exercise at three increasing workloads (in W) while maintaining a pedal rate of 60-70 rpm. Each workload trial lasted 5 min. The maximum of the three workloads did not exceed a heart rate of 170 beats/min. By linear extrapolation of the workload-heart rate relationship to each subject's age-related predicted maximum heart, the subject's percentage of maximal physical work capacity (PWCmax) was determined.
On a subsequent study day, the relative contributions of oral vs. nasal breathing were measured at rest and during incrementally graded submaximal exercise on the cycle ergometer (10% increments from 0-60% PWCmax for each subject).
Each subject was fitted with a nasal mask similar to that used in pulmonary sleep laboratories and modified to allow insertion of a mass flowmeter. Total ventilation ( E) was determined by respiratory inductance plethysmography (calibrated by spirometry). Bands were fixed to the subject's torso with adhesive tape and calibrated. Oral airflow was determined as the difference between total and nasal (nasal mask). Subjects maintained a 60- to 70-rpm pedal rate at each 10% increment of effort for 2 min.
To calibrate volumes obtained from respiratory inductance plethysmography with the nasal flowmeter, the researchers compared both signals to a volume signal from a spirometer through which the subject rebreathed postexercise via the nose only with the obstructed mouthpiece (mouth plug) in place. This calibration was conducted postexercise so that the subject would be as unbiased as possible with regard to nasal vs. oral breathing during the exercise session.
Immediately after measurements of oral-nasal breathing during exercise (within 15 min), measurements of airway resistance in the body plethysmograph were made while the subject panted through a mouthpiece (with nose plug) and then through the nasal mask (with mouth plug); Rnose was then determined as the absolute difference between the mouthpiece and nasal mask measure of total airway resistance. Also, after the exercise session (within 15 min postexercise), subjects performed maximal inspiratory flow maneuvers via their nose by slowly exhaling to near residual volume and then rapidly inhaling through their nose at maximal effort with the nose mask and mouth plug in place. MIFnose associated with these maneuvers was determined as the peak flow for each maneuver.
Group comparisons, i.e., Caucasians vs. African-Americans and men vs. women, for all variables reported were made by independent sample t-test. Due to the limited data set, the researchers did not consider interactions between variables for this exploratory analysis. Statistical criteria for a variable to enter and stay in the stepwise model was set at P = 0.15.
The researchers found the following:
- In all subjects studied, E increased linearly with increasing workload to 60% PWCmax, whereas nasal ventilation increased more slowly with increasing workload. Only forced vital capacity and MIFnose were significantly different between the two groups.
- There was a tendency for Rnose to be less in the African-Americans vs. the Caucasians.
- Rnose tended toward a negative correlation with MIFnose.
- AT 20% and 60% PWCmax, Caucasians had significantly less nasal contribution to breathing than African-Americans.
- There was a tendency toward a racial difference at 40% PWCmax.
- Women had a significantly less PWCmax, compared with men, and, as a result, also had a lesser E at 60% PWCmax.
- Below E =35 liters/min, there was considerable variation in percent nasal contribution to breathing (30-100%), with African-Americans clearly having a greater nasal contribution than Caucasians. Above E = 35 liters/min, the percent nasal contribution dropped to <40% in all of the Caucasians, whereas four of the African-Americans maintained percent nasal contributions of >40%.
As have others before them, the researchers found that the contribution of nasal breathing to E diminishes with increasing exercise effort. However, they also found that nasal ventilation during exercise varies as a function of both race and gender.
African-Americans have a greater nasal contribution to breathing during exercise than Caucasians. It may be that this interracial difference is due to the former's ability to achieve greater maximal flow rates through their nose, although this dependence requires further investigation.
At relative exercise efforts, women also had a greater nasal contribution to breathing during exercise than men. This gender difference is explained by the fact that the women achieved lower E than men at a given percentage of their maximum work capacity. Because oral augmentation during exercise was shown to be a function of E, the women did not need to augment their breathing orally until much later in their relative work effort.
These racial and gender-related differences in route of breathing during exercise may be important for determining relative risks of individuals to environmental or occupational exposures of potentially toxic gases or particulate matter.
Source: August 2003 edition of the Journal of Applied Physiology.
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.