Dyspnea on exertion in obese women: Association with an increased oxygen cost of breathing
ABSTRACT Although exertional dyspnea in obesity is an important and prolific clinical concern, the underlying mechanism remains unclear.
To investigate whether dyspnea on exertion in otherwise healthy obese women was associated with an increase in the oxygen cost of breathing or cardiovascular deconditioning.
Obese women with and without dyspnea on exertion participated in two independent experiments (n = 16 and n = 14). All participants underwent pulmonary function testing, hydrostatic weighing, ratings of perceived breathlessness during cycling at 60 W, and determination of the oxygen cost of breathing during eucapnic voluntary hyperpnea at 40 and 60 L/min. Cardiovascular exercise capacity, fat distribution, and respiratory mechanics were determined in 14 women in experiment 2. Data were analyzed between groups by independent t test, and the relationship between the variables was determined by regression analysis.
In both experiments, breathlessness during 60 W cycling was markedly increased in over 37% of the obese women (P < 0.01). Age, height, weight, lung function, and %body fat were not different between the groups in either experiment. In contrast, the oxygen cost of breathing was significantly (P < 0.01) and markedly (38-70%) greater in the obese women with dyspnea on exertion. The oxygen cost of breathing was significantly (P < 0.001) correlated with the rating of perceived breathlessness obtained during the 60 W exercise in experiment 1 (r(2) = 0.57) and experiment 2 (r(2) = 0.72). Peak cardiovascular exercise capacity, fat distribution, and respiratory mechanics were not different between groups in experiment 2.
Dyspnea on exertion is prevalent in otherwise healthy obese women, which seems to be strongly associated with an increased oxygen cost of breathing. Exercise capacity is not reduced in obese women with dyspnea on exertion.
- SourceAvailable from: Denis E O'Donnell
[Show abstract] [Hide abstract]
- "In this study, ˙ V O 2resp (estimated as the change in ˙ V O 2 from rest during eucapnic voluntary hyperventilation) was 40–70% higher in OB women with vs. without exertional breathlessness (defined as a Borg rating of perceived breathlessness of ≥4 and ≤2 units at a standardized submaximal cycle work rate of 60 watts, respectively), even though ventilatory, breathing pattern, dynamic operating lung volume and esophageal pressure-derived respiratory mechanical/muscular responses to exercise were no different between-groups (Babb et al., 2008a; Wood et al., 2008). In this regard, the positive correlation between ˙ V O 2resp and Borg ratings of exertional breathlessness reported by Babb et al. (2008a) could not be easily accounted for. Furthermore, it is difficult to reconcile both the mean and correlative results of this study with the following observations: (1) experimentally decreasing the WOB and ˙ V O 2resp did not alleviate the intensity of perceived breathlessness during constant-load cycle exercise in patients with stable congestive heart failure (O'Donnell et al., 1999) and (2) increases in the WOB and ˙ V O 2resp are not obligatory to provoke breathlessness under controlled experimental conditions (Banzett et al., 1989, 1990; Gandevia et al., 1993). "
ABSTRACT: The healthy human respiratory system has impressive ventilatory reserve and can easily meet the demands placed upon it by strenuous exercise. Several acute physiological adaptations during exercise ensure harmonious neuromechanical coupling of the respiratory system, which allow healthy humans to reach high levels of ventilation without perceiving undue respiratory discomfort (breathlessness). However, in certain circumstances, such as pregnancy, obesity and natural aging, ventilatory reserve becomes diminished and exertional breathlessness is present. In this review, we focus on what is known about the mechanisms of increased activity-related breathlessness in these populations. Notwithstanding the obvious physiological differences between the three conditions, they share some common perceptual and ventilatory responses to exercise. Breathlessness intensity ratings (described as an increased "sense of effort") are consistently higher than normal at any given submaximal power output; and central motor drive to the respiratory muscles is consistently increased, reflecting increased ventilatory stimulation. The increased contractile respiratory muscle effort required to support the increased ventilatory requirements of exercise remains the most plausible source of increased activity-related breathlessness in pregnant, obese and elderly humans. In all three conditions, static and dynamic respiratory mechanical/muscular function is, to some extent, altered or impaired. Nevertheless, breathlessness intensity ratings are not significantly increased (compared to normal) at any given exercise ventilation in any of these three conditions. This strongly suggests that respiratory mechanical/muscular factors, per se, may be less important in the genesis of breathlessness. Moreover, in pregnancy and obesity, we present evidence that effective physiological adjustments exist to counterbalance the potentially negative sensory consequences of the altered respiratory mechanical/muscular function peculiar to these conditions.Respiratory Physiology & Neurobiology 06/2009; 167(1):87-100. DOI:10.1016/j.resp.2009.01.011 · 1.97 Impact Factor
Conference Paper: The IGBT with monolithic overvoltage protection circuit[Show abstract] [Hide abstract]
ABSTRACT: A novel IGBT (insulated-gate bipolar transistor) with a monolithic overvoltage protection circuit has been developed to obtain high resistance to overvoltage stress. This device is characterized by novel integration of an avalanche diode with an IGBT structure. The conventional IGBT process can be used to fabricate this device without any additional photomasks. Since it exhibits a large safe operating area, this device can be applied not only to a soft switching application like a voltage resonant circuit but also to a hard switching application like a snubberless inductive load circuitPower Semiconductor Devices and ICs, 1993. ISPSD '93., Proceedings of the 5th International Symposium on; 06/1993
Conference Paper: Optical beam forming and steering for phased-array antenna[Show abstract] [Hide abstract]
ABSTRACT: Application of photonics in beam forming and steering for phased-array antennas is addressed in this paper. The feasibility of photonics in space communications systems centers around the basic issues such as the need for photonics and derived benefits, overall performance, and complexity and cost of implementation. Several optical beam forming and steering payloads are assessed for their capability and technology feasibility. Also included are the results of demonstrated proof-of-concept (POC) schemesTelesystems Conference, 1993. 'Commercial Applications and Dual-Use Technology', Conference Proceedings., National; 07/1993