Influence of genetic variation of the ß2-adrenergic receptor on lung diffusion in patients with cystic fibrosis.

RATIONALE: Cystic fibrosis (CF) is a disease that adversely affects the lung resulting in a reduction in lung diffusion. Stimulation of the ß(2)-adrenergic receptors mediates mucociliary clearance and bronchodilation. We sought to determine the influence of an inhaled ß-agonist on the diffusing capacity of the lungs for carbon monoxide (DLCO), alveolar-capillary membrane conductance (D(M)), pulmonary capillary blood volume (Vc), and peripheral oxygen saturation (SaO(2)) in subjects with CF, when compared to matched healthy subjects, according to genetic variation of the ß(2)-adrenergic receptor (ADRB2). METHODS: To determine this we recruited 18 subjects with CF and 20 healthy subjects (age = 23 ± 7 vs. 24±4years; ht = 168 ± 8 vs. 174 ± 12 cm; wt = 64 ± 16 vs. 70 ± 13 kg; BMI = 23 ± 4 vs. 23±3 kg/m(2); FEV(1) = 72 ± 27 vs. 92 ± 12%pred; VO(2peak) = 45 ± 25 vs. 99 ± 24%pred, p < 0.05 for FEV(1) and VO(2peak), mean ± SD, for CF and healthy, respectively). The study involved measurement of DLCO, D(M), V(C) and SaO(2) before and 30, 60, and 90 min following the administration of inhaled albuterol. Subjects were stratified according to genetic variation of ADRB2, Gln(27)Gln vs. Glu(27)Glu/Gln(27)Glu. RESULTS: Within the healthy group, there were no differences in DLCO, D(M), V(C), D(M)/V(C) at baseline or in response to albuterol according to genetic variation of the ADRB2 at amino acid 27. Within the CF group, the Glu(27)Glu/Gln(27)Glu group had higher D(M)/V(C) and SaO(2) when compared to the Gln(27)Gln group at baseline (p < 0.05). Both genotype groups demonstrated a significant decline in V(C) and an improvement in D(M)/V(C) and SaO(2) in response to albuterol. Subjects with the Glu(27) genotype experienced a greater improvement in D(M)/V(C) with albuterol when compared to subjects homozygous for Gln at amino acid 27. CONCLUSION: These results suggest that there are differences in lung diffusion and peripheral SaO(2) according to genetic variation of the ADRB2 at position 27 which could play a potential role in dosing options or adjustments that may be required according to genotype.

Glycemic control influences lung membrane diffusion and oxygen saturation in exercise-trained subjects with type 1 diabetes: alveolar-capillary membrane conductance in type 1 diabetes.

Lung diffusing capacity (DLCO) is influenced by alveolar-capillary membrane conductance (D (M)) and pulmonary capillary blood volume (V (C)), both of which can be impaired in sedentary type 1 diabetes mellitus (T1DM) subjects due to hyperglycemia. We sought to determine if T1DM, and glycemic control, affected DLNO, DLCO, D (M), V (C) and SaO(2) during maximal exercise in aerobically fit T1DM subjects. We recruited 12 T1DM subjects and 18 non-diabetic subjects measuring DLNO, DLCO, D (M), and V (C) along with SaO(2) and cardiac output (Q) at peak exercise. The T1DM subjects had significantly lower DLCO/Q and D (M)/Q with no difference in Q, DLNO, DLCO, D (M), or V (C) (DLCO/Q = 2.1 ± 0.4 vs. 1.7 ± 0.3, D (M)/Q = 2.8 ± 0.6 vs. 2.4 ± 0.5, non-diabetic and T1DM, p < 0.05). In addition, when considering all subjects there was a relationship between DLCO/Q and SaO(2) at peak exercise (r = 0.46, p = 0.01). Within the T1DM group, the optimal glycemic control group (HbA1c <7%, n = 6) had higher DLNO, DLCO, and D (M)/Q than the poor glycemic control subjects (HbA1c ≥ 7%, n = 6) at peak exercise (DLCO = 38.3 ± 8.0 vs. 28.5 ± 6.9 ml/min/mmHg, DLNO = 120.3 ± 24.3 vs. 89.1 ± 21.0 ml/min/mmHg, D (M)/Q = 3.8 ± 0.8 vs. 2.7 ± 0.2, optimal vs. poor control, p < 0.05). There was a negative correlation between HbA1c with DLCO, D (M) and D (M)/Q at peak exercise (DLCO: r = -0.70, p = 0.01; D (M): r = -0.70, p = 0.01; D (M)/Q: r = -0.68, p = 0.02). These results demonstrate that there is a reduction in lung diffusing capacity in aerobically fit athletes with T1DM at peak exercise, but suggests that maintaining near-normoglycemia potentially averts lung diffusion impairments.

Exhaled breath condensate detects baseline reductions in chloride and increases in response to albuterol in cystic fibrosis patients.

Impaired ion regulation and dehydration is the primary pathophysiology in cystic fibrosis (CF) lung disease. A potential application of exhaled breath condensate (EBC) collection is to assess airway surface liquid ionic composition at baseline and in response to pharmacological therapy in CF. Our aims were to determine if EBC could detect differences in ion regulation between CF and healthy and measure the effect of the albuterol on EBC ions in these populations. Baseline EBC Cl(-), DLCO and SpO2 were lower in CF (n = 16) compared to healthy participants (n = 16). EBC Cl(-) increased in CF subjects, while there was no change in DLCO or membrane conductance, but a decrease in pulmonary-capillary blood volume in both groups following albuterol. This resulted in an improvement in diffusion at the alveolar-capillary unit, and removal of the baseline difference in SpO2 by 90-minutes in CF subjects. These results demonstrate that EBC detects differences in ion regulation between healthy and CF individuals, and that albuterol mediates increases in Cl(-) in CF, suggesting that the benefits of albuterol extend beyond simple bronchodilation.

Genetic variation of SCNN1A influences lung diffusing capacity in cystic fibrosis.

INTRODUCTION: Epithelial Na channels (ENaCs) play a crucial role in ion and fluid regulation in the lung. In cystic fibrosis (CF), Na hyperabsorption results from ENaC overactivity, leading to airway dehydration. Previous work has demonstrated functional genetic variation of SCNN1A (the gene encoding the ENaC α-subunit), manifesting as an alanine (A) to threonine (T) substitution at amino acid 663, with the αT663 variant resulting in a more active channel. METHODS: We assessed the influence of genetic variation of SCNN1A on the diffusing capacity of the lungs for carbon monoxide (DLCO) and nitric oxide (DLNO), together with alveolar-capillary membrane conductance (DM), pulmonary capillary blood volume, and alveolar volume (VA) at rest and during peak exercise in 18 patients with CF (10 homozygous for αA663 (AA group) and 8 with at least one T663 allele (AT/TT group)). Because of the more active channel, we hypothesized that the AT/TT group would show a greater increase in DLCO, DLNO, and DM with exercise because of exercise-mediated ENaC inhibition and subsequent attenuation of Na hyperabsorption. RESULTS: The AT/TT group had significantly lower pulmonary function, weight, and body mass index than the AA group. Both groups had similar peak workloads, relative peak oxygen consumptions, and cardiopulmonary responses to exercise. The AT/TT group demonstrated a greater increase in DLNO, DLNO/VA, and DM in response to exercise (% increases: DLNO = 18 ± 11 vs 41 ± 38; DLNO/VA = 14 ± 21 vs 40 ± 37; DM = 15 ± 11 vs 41 ± 38, AA vs AT/TT, respectively). There were no differences between groups in absolute diffusing capacity measures at peak exercise. CONCLUSION: These results suggest that genetic variation of the α-subunit of ENaC differentially affects the diffusing capacity response to exercise in patients with CF.

Effects of an inhaled ß2-agonist on cardiovascular function and sympathetic activity in healthy subjects.

STUDY OBJECTIVE: To determine the effect of a short-acting, inhaled ß(2)-adrenergic receptor agonist, albuterol sulfate, administered by nebulization, on cardiovascular function and sympathetic activity in healthy individuals. DESIGN: Prospective, placebo-controlled, single-blind, crossover study. SETTING: University research center. SUBJECTS: Seventeen healthy subjects. INTERVENTION: After a screening visit to rule out cardiovascular abnormalities and anemia, each subject participated in two more separate visits. At the second visit, they were administered a single dose of either nebulized albuterol sulfate 2.5 mg diluted in 3 ml of normal saline or placebo (3 ml of normal saline). One week later, subjects returned for their third visit and received the other treatment. MEASUREMENTS AND MAIN RESULTS: At the two study visits, before and 30, 60, and 90 minutes after administration of albuterol or placebo, we measured plasma catecholamine levels (epinephrine and norepinephrine), cardiac output, heart rate, and systolic and diastolic blood pressure, and we calculated stroke volume, mean arterial pressure, and systemic vascular resistance (SVR). Inhaled placebo resulted in no significant change overall in any of the measured or calculated cardiovascular parameters. Compared with baseline values, albuterol administration after 30, 60, and 90 minutes, increased cardiac output (mean ± SD 4.2 ± 1.1, 4.4 ± 1.3, and 4.3 ± 1.1 L/min, respectively, vs 3.6 ± 1.0 L/min) and stroke volume (51 ± 15, 56 ± 14, and 56 ± 13 ml, respectively, vs 46 ± 12 ml), did not significantly change blood pressure, and decreased SVR (1401 ± 432, 1393 ± 424, and 1384 ± 391 dynes•sec/cm(5), respectively, vs 1661 ± 453 dynes•sec/cm(5)) (p<0.05 for all comparisons). Heart rate was significantly changed with both albuterol and placebo, but only at 30 minutes after treatment. Albuterol, but not placebo, also increased plasma norepinephrine levels. CONCLUSION: In these healthy subjects, administration of a nebulized ß(2)-agonist resulted in enhanced ventricular function and a decrease in SVR, suggesting peripheral vasodilation. In addition, the increase in norepinephrine level with albuterol, but not placebo, may have important implications in patients with known cardiovascular disease.

Genetic variation of the alpha subunit of the epithelial Na+ channel influences exhaled Na+ in healthy humans.

Epithelial Na(+) channels (ENaC) are located in alveolar cells and are important in ß(2)-adrenergic receptor-mediated lung fluid clearance through the removal of Na(+) from the alveolar airspace. Previous work has demonstrated that genetic variation of the alpha subunit of ENaC at amino acid 663 is important in channel function: cells with the genotype resulting in alanine at amino acid 663 (A663) demonstrate attenuated function when compared to genotypes with at least one allele encoding threonine (T663, AT/TT). We sought to determine the influence of genetic variation at position 663 of ENaC on exhaled Na(+) in healthy humans. Exhaled Na(+) was measured in 18 AA and 13 AT/TT subjects (age=27±8 years vs. 30±10 years; ht.=174±12 cm vs. 171±10 cm; wt.=68±12 kg vs. 73±14 kg; BMI=22±3 kg/m(2) vs. 25±4 kg/m(2), mean±SD, for AA and AT/TT, respectively). Measurements were made at baseline and at 30, 60 and 90 min following the administration of a nebulized ß(2)-agonist (albuterol sulfate, 2.5 mg diluted in 3 ml normal saline). The AA group had a higher baseline level of exhaled Na(+) and a greater response to ß(2)-agonist stimulation (baseline=3.1±1.8 mmol/l vs. 2.3±1.5 mmol/l; 30 min-post=2.1±0.7 mmol/l vs. 2.2±0.8 mmol/l; 60 min-post=2.0±0.5 mmol/l vs. 2.3±1.0 mmol/l; 90 min-post=1.8±0.8 mmol/l vs. 2.6±1.5 mmol/l, mean±SD, for AA and AT/TT, respectively, p<0.05). The results are consistent with the notion that genetic variation of ENaC influences ß(2)-adrenergic receptor stimulated Na(+) clearance in the lungs, as there was a significant reduction in exhaled Na(+) over time in the AA group.

Genetic variation of αENaC influences lung diffusion during exercise in humans.

Exercise, decompensated heart failure, and exposure to high altitude have been shown to cause symptoms of pulmonary edema in some, but not all, subjects, suggesting a genetic component to this response. Epithelial Na(+) Channels (ENaC) regulate Na(+) and fluid reabsorption in the alveolar airspace in the lung. An increase in number and/or activity of ENaC has been shown to increase lung fluid clearance. Previous work has demonstrated common functional genetic variants of the α-subunit of ENaC, including an A→T substitution at amino acid 663 (αA663T). We sought to determine the influence of the T663 variant of αENaC on lung diffusion at rest and at peak exercise in healthy humans. Thirty healthy subjects were recruited for study and grouped according to their SCNN1A genotype [n=17 vs. 13, age=25±7 years vs. 30±10 years, BMI=23±4 kg/m(2) vs. 25±4 kg/m(2), V(O2 peak) = 95±30%pred. vs. 100±31%pred., mean±SD, for AA (homozygous for αA663) vs. AT/TT groups (at least one αT663), respectively]. Measures of the diffusing capacity of the lungs for carbon monoxide (DL(CO)), the diffusing capacity of the lungs for nitric oxide (DL(NO)), alveolar volume (V(A)), and alveolar-capillary membrane conductance (D(M)) were taken at rest and at peak exercise. Subjects expressing the AA polymorphism of ENaC showed a significantly greater percent increase in DL(CO) and DL(NO), and a significantly greater decrease in systemic vascular resistance from rest to peak exercise than those with the AT/TT variant (DL(CO)=51±12% vs. 36±17%, DL(NO)=51±24% vs. 32±25%, SVR=-67±3 vs. -50±8%, p<0.05). The AA ENaC group also tended to have a greater percent increase in DL(CO)/VA from rest to peak exercise, although this did not reach statistical significance (49±26% vs. 33±26%, p=0.08). These results demonstrate that genetic variation of the α-subunit of ENaC at amino acid 663 influences lung diffusion at peak exercise in healthy humans, suggesting differences in alveolar Na(+) and, therefore, fluid handling. These findings could be important in determining who may be susceptible to pulmonary edema in response to various clinical or environmental conditions.

Impaired lung diffusing capacity for nitric oxide and alveolar-capillary membrane conductance results in oxygen desaturation during exercise in patients with cystic fibrosis.

BACKGROUND: Exercise has been shown to be beneficial for patients with cystic fibrosis (CF), but for some CF patients there is a risk of desaturation, although the predicting factors are not conclusive or reliable. We sought to determine the relationship between the diffusion capacity of the lungs for nitric oxide and carbon monoxide (DLNO and DLCO) and the components of DLCO: alveolar-capillary membrane conductance (D(M)), and pulmonary capillary blood volume (V(C)) on peripheral oxygen saturation (SaO(2)) at rest and during exercise in CF. METHODS: 17 mild/moderate CF patients and 17 healthy subjects were recruited (age=26±7 vs. 23±8 years, ht=169±8 vs. 166±8 cm, wt=65±9 vs. 59±8 kg, BMI=23±3 vs. 22±3 kg/m(2), VO(2PEAK)=101±36 vs. 55±25%pred., FEV(1)=92±22 vs. 68±25%pred., for healthy and CF, respectively, mean±SD, VO(2PEAK) and FEV(1) p<0.001). Subjects performed incremental cycle ergometry to exhaustion with continuous monitoring of SaO(2) and measures of DLNO, DLCO, D(M) and V(C) at each stage. RESULTS: CF patients had a lower SaO(2) at rest and peak exercise (rest=98±1 vs. 96±1%, peak=97±2 vs. 93±5%, for healthy and CF, respectively, p<0.01). At rest, DLNO, DLCO, D(M) were significantly lower in the CF group (p<0.01). The difference between groups was augmented with exercise (DLNO=117±4 vs. 73±3ml/min/mmHg; DLCO=34±8 vs. 23±8ml/min/mmHg; D(M)=50±1 vs. 34±1, p<0.001, for healthy and CF respectively). Peak SaO(2) was related to resting DLNO in CF patients (r=0.65, p=0.003). CONCLUSIONS: These results suggest a limitation in exercise-mediated increases in membrane conductance in CF which may contribute to a drop in SaO(2) and that resting DLNO can account for a large portion of the variability in SaO(2).

Variability in measures of exhaled breath na, influence of pulmonary blood flow and salivary na.

The assessment of inflammatory markers and ions in exhaled breath condensate (EBC) is being utilized more frequently in diseases such as asthma and cystic fibrosis with marked variability in EBC measures, including those of exhaled Na(+). We sought to determine if variability in exhaled Na(+) was due to differences in pulmonary blood flow (PBF) or Na(+) in the mouth (salivary Na(+)). We measured exhaled Na(+) three times with coinciding sampling of salivary Na(+) and assessment of PBF (using acetylene rebreathing) in 13 healthy subjects (54% female, age = 27 ± 7 yrs., ht. = 172 ± 10 cm, wt. = 70 ± 21 kg, BMI = 22 ± 7 kg/m(2) mean ± SD). Exhaled Na(+) averaged 2.7 ± 1.2 mmol/l, and salivary Na(+) averaged 5.51 ± 4.58 mmol/l. The coefficients of variation across all three measures in all 13 subjects averaged 30% for exhaled Na(+) and 83% for salivary Na(+), within subjects the variability across the three measures averaged 30% for exhaled Na(+) and 38% for salivary Na(+). Across all three measures in all 13 subjects the relationship between PBF and exhaled Na(+) averaged 0.027 (P = 0.87), and the relationship between salivary Na(+) and exhaled Na(+) concentrations averaged 0.59 (P = 0.001). Also, we sought to determine the relationship between exhaled Na(+) and serum Na(+) in an addition 20 subjects. There was a moderate and significant relationship between serum Na(+) and exhaled Na(+) (r = 0.37, P = 0.04). These findings suggest there that the variability in exhaled Na(+) is caused, at least in part, by droplet formation from within the mouth as turbulent air passes through and that there is a flux of ions from the pulmonary blood into the airways.

Glycemic status affects cardiopulmonary exercise response in athletes with type I diabetes.

PURPOSE: This study aimed to (a) examine the influence of type I diabetes on the cardiopulmonary exercise response in trained subjects and (b) determine whether glycemic control affects these responses. METHODS: The cardiopulmonary responses to maximal incremental cycle ergometry were compared in 12 Ironman triathletes with type I diabetes and 10 age- and sex-matched control subjects without diabetes. Athletes with type I diabetes were then stratified into low- (glycosylated hemoglobin (HbA1c) < 7%, n = 5) and high-HbA1c (HbA1c > 7%, n = 7) groups for comparison. Cardiac output, stroke volume, arterial blood pressure, and calculated systemic vascular resistance along with airway function were measured at rest and during steady-state exercise. RESULTS: During peak exercise HR, stroke volume and cardiac output were not different between the groups with and without diabetes; however, forced expiratory flow at 50% of the forced vital capacity was lower in subjects with diabetes (P < 0.05). Within the group with diabetes, HbA1c was lower in the low-HbA1c versus high-HbA1c group (6.5 +/- 0.3 vs 7.8 +/- 0.4, respectively; P < 0.05), but training volume was not different. At rest, the low-HbA1c group had greater cardiac output and lower systemic vascular resistance than the high-HbA1c group, and all pulmonary function measurements were greater in the low-HbA1c group (P < 0.05). During peak exercise, the VO2, workload, HR, stroke volume, and cardiac output were greater in the low-HbA1c versus the high-HbA1c group (P < 0.05). In addition, all indices of pulmonary function were higher in the low-HbA1c group (P < 0.05). Finally, within the subjects with diabetes, there was a weak inverse correlation between HbA1c and exercise training volume (r2 = -0.352) and stroke volume (r2 = -0.339). These data suggest that highly trained individuals with type I diabetes can achieve the same cardiopulmonary exercise responses as trained subjects without diabetes, but these responses are reduced by poor glycemic control.