Effects of age on pulmonary perfusion heterogeneity measured by magnetic resonance imaging.

Normal aging is associated with a decline in pulmonary function and efficiency of gas exchange, although the effects on the spatial distribution of pulmonary perfusion are poorly understood. We hypothesized that spatial pulmonary perfusion heterogeneity would increase with increasing age. Fifty-six healthy, nonsmoking subjects (ages 21-76 yr) underwent magnetic resonance imaging with arterial spin labeling (ASL) using a Vision 1.5-T whole body scanner (Siemens Medical Systems, Erlangen, Germany). ASL uses a magnetically tagged bolus to generate perfusion maps where signal intensity is proportional to regional pulmonary perfusion. The spatial heterogeneity of pulmonary blood flow was quantified by the relative dispersion (RD = SD/mean, a global index of heterogeneity) of signal intensity for voxels within the right lung and by the fractal dimension (D(s)). There were no significant sex differences for RD (P = 0.81) or D(s) (P = 0.43) when age was considered as a covariate. RD increased significantly with increasing age by approximately 0.1/decade until age 50-59 yr, and there was a significant positive relationship between RD and age (R = 0.48, P < 0.0005) and height (R = 0.39, P < 0.01), but not body mass index (R = 0.07, P = 0.67). Age and height combined in a multiple regression were significantly related to RD (R = 0.66, P < 0.0001). There was no significant relationship between RD and spirometry or arterial oxygen saturation. D(s) was not related to age, height, spirometry, or arterial oxygen saturation. The lack of relationship between age and D(s) argues against an intrinsic alteration in the pulmonary vascular branching with age as being responsible for the observed increase in global spatial perfusion heterogeneity measured by the RD.

The effect of incomplete acetylene washout on cardiac output measurement using open circuit acetylene uptake.

The open circuit acetylene uptake method is a useful non-invasive means of measuring cardiac output. However, because of accumulation of inhaled acetylene in tissues, the cardiac output uptake is underestimated, if residual acetylene is not allowed to wash out completely in between measurements. We determined the effect of applying a correction factor that estimates mixed venous acetylene concentration from endtidal values to the calculation of cardiac output. This accounts for mixed venous acetylene present during measurements made before complete washout. Six healthy subjects performed steady-state exercise at approximately 30% and 60% of V(O2 max). Cardiac output measurements were made at each exercise intensity using the open circuit acetylene uptake method (inspired [acetylene] approximately 1%), with the first and last measurements having no detectible levels of acetylene in expired gas (reference measurement). Data were also obtained with immediate pre-measurement endtidal concentrations ranging from 3% to 15% of the inspired [acetylene], in random order in between. Oxygen consumption, carbon dioxide production and heart rate did not change significantly during testing at each exercise intensity. Reference cardiac output also did not change significantly and averaged 11.1+/-0.8 L/min at 30% of V(O2 max) and 16.5+/-2.0 L/min at 60% of V(O2 max). Uncorrected cardiac output measurements progressively underestimated cardiac output by 15% at the 3% of inspired endtidal [acetylene] and by over 50% at 15% [acetylene] (p<0.0001). However, when corrected for residual endtidal [acetylene], cardiac outputs were not significantly different from the reference measurements. The results of this study suggest that by accounting for residual endtidal acetylene in mixed venous blood, cardiac output can be accurately measured even when washout of acetylene is incomplete, allowing measurements as often as every 10-15 s.

Oxygen consumption during maximal exercise in Fischer 344 x Brown Norway F1 hybrid rats.

We characterized O2 consumption (VO2) during treadmill exercise in 12-, 24-, and 35-month-old Fischer 344 x Brown Norway F1 hybrid (F344BNF1) rats. When accounting for differences in body mass (Mb), (O2)peak decreased by 10% and 33% in 24- and 35-month-old rats, respectively, compared with rats at 12 months (analysis of covariance, p < .01). O2 cost per unit work at VO2peak (i.e., VO2peak/work) was greater in 35-month-old rats compared with 12- and 24-month-old rats (p < .001). During submaximal exercise, the O2 cost was greater in 24- and 35-month-old than 12-month-old rats (p < .01). Analysis of covariance revealed similar patterns irrespective of differences in Mb or lean Mb as covariates. The underlying mechanism responsible for increasing O2 consumption in aged F344BNF1 rats during exercise, although partly explained by mechanical inefficiencies of locomotion, still remains to be determined.

Cancer rehabilitation education during physical medicine and rehabilitation residency: preliminary data regarding the quality and quantity of experiences.

OBJECTIVE: The purpose of this study was to gather descriptive information from residency program directors regarding characteristics of the education and experiences of resident physicians in oncology rehabilitation. DESIGN: The program directors responded to a 28-question survey. Information collected included general descriptors of residency programs, oncology rehabilitation services lines within the institution, educational and clinical opportunities for trainees, and perceptions of quality for oncology experiences. RESULTS: Thirty-eight responses, with a response rate of 48%, were recorded. Thirty-two percent of the programs did not have any dedicated faculty for cancer rehabilitation. A majority of the respondents felt that cancer rehabilitation should be an important component of the curriculum. Sixty-six percent of the programs admitted only one to two cancer diagnoses to their inpatient units per week, and 26% had outpatient clinics that focused specifically on rehabilitation needs for oncology patients. A majority of the programs felt that experiences were only average and that residents do not receive adequate exposure to cancer rehabilitation during their training. CONCLUSIONS: Although cancer rehabilitation is considered an important area of education, quality and quantity of experiences may be improved. Several opportunities may exist to improve such exposure in anticipation of serving the functional needs for a growing population of cancer survivors.

Pulmonary blood flow heterogeneity during hypoxia and high-altitude pulmonary edema.

Uneven hypoxic pulmonary vasoconstriction has been proposed to expose parts of the pulmonary capillary bed to high pressure and vascular injury in high-altitude pulmonary edema (HAPE). We hypothesized that subjects with a history of HAPE would demonstrate increased heterogeneity of pulmonary blood flow during hypoxia. A functional magnetic resonance imaging technique (arterial spin labeling) was used to quantify spatial pulmonary blood flow heterogeneity in three subject groups: (1) HAPE-susceptible (n = 5), individuals with a history of physician-documented HAPE; (2) HAPE-resistant (n = 6), individuals with repeated high-altitude exposure without illness; and (3) unselected (n = 6), individuals with a minimal history of altitude exposure. Data were collected in normoxia and after 5, 10, 20, and 30 minutes of normobaric hypoxia FI(O(2)) = 0.125. Relative dispersion (SD/mean) of the signal intensity was used as an index of perfusion heterogeneity. Oxygen saturation was not different between groups during hypoxia. Relative dispersion was not different between groups (HAPE-susceptible 0.94 +/- 0.05, HAPE-resistant 0.94 +/- 0.05, unselected 0.87 +/- 0.06; means +/- SEM) during normoxia, but it was increased by hypoxia in HAPE-susceptible (to 1.10 +/- 0.05 after 30 minutes, p < 0.0001) but not in HAPE-resistant (0.91 +/- 0.05) or unselected subjects (0.87 +/- 0.05). HAPE-susceptible individuals have increased pulmonary blood flow heterogeneity in acute hypoxia, consistent with uneven hypoxic pulmonary vasoconstriction.

Does gender affect human pulmonary gas exchange during exercise?

Women may experience greater pulmonary gas exchange impairment during exercise than men. To test this we used the multiple inert gas elimination technique to study eight women and seven men matched for age, height and (O(2) max) ( approximately 48 ml x kg(-1) min(-1)) during normoxic and hypoxic (inspired P(O(2))= 95 Torr) cycle exercise. Resting lung function was similar between the sexes, except for a lower carbon monoxide diffusing capacity (DL(CO)) in women (P < 0.05). Arterial P(O(2)),P(CO(2)) and alveolar-arterial O(2) difference (A-aD(O(2))) were not significantly different in men and women. Despite a lower diffusing capacity for O(2) (DL(O(2))) in women, the ratio DL(O(2))/beta (which estimates pulmonary end-capillary diffusion equilibrium) was similar between men and women and estimates of diffusion limitation during hypoxic exercise were not different between the sexes. Ventilation-perfusion inequality (described by the second moment of the perfusion distribution, logSD increased during both normoxic and hypoxic exercise. Surprisingly, logSD values were slightly lower for women under all conditions (P < 0.05), but this did not significantly affect gas exchange. These data indicate that these active women, despite a lower DL(CO) and DL(O(2)), do not experience greater exercise-induced abnormalities in gas exchange than men matched for age, height, aerobic capacity and lung size. Possibly fitness level and lung size are more important in determining whether or not pulmonary gas exchange impairment occurs during exercise than sex per se.