Rebreathing Method Research Articles

C3. Cardiovascular changes from pre-pregnancy to early pregnancy in relation to viability of pregnancy

Introduction: Inadequate cardiovascular adaptation to pregnancy has been postulated as a potential cause or consequence of early pregnancy loss. We sought to investigate pre- and early pregnancy cardiovascular function in women with a viable pregnancy beyond the first trimester, and those suffering a first trimester pregnancy loss.Methods: We recruited healthy women trying for pregnancy without assisted reproductive technology into an observational pre-conception study, and recorded pregnancy loss as a clinical endpoint. The participants underwent comprehensive cardiovascular testing, including assessments of cardiac output (CO) using a noninvasive gas rebreathing method in lying and standing position. CO values were adjusted for body surface area and reported as cardiac index (CIdx). Participants that conceived a pregnancy were assessed at 6 weeks gestation with repeat CO and CIdx measurements, and a fetal viability scan. We compared change (delta) in CO and CIdx between pre-pregnancy and 6 weeks gestation between participants who had sonographic diagnosis of pregnancy of unknown viability (PUV) and subsequently miscarried (Group 1 – 11 women), participants who had a normal scan at 6 weeks gestation but subsequently miscarried (Group 2 – 17 women) and 25 matched controls who had normal 6 week scan and viable pregnancy beyond the first trimester.Results: From 292 participants recruited pre-pregnancy, 176 pregnancies were conceived within 16 months. Fifty-four pregnancies miscarried in the first trimester, 26 before their first scheduled post conception visit at 6 weeks. In the 28 women in whom cardiovascular and ultrasound data were obtainable at 6 weeks, there was no significant difference between delta lying CO (p =0.3876, 95%CI–1.73 to 0.73; p = 0.1781, 95%CI–1.326 to 0.267) and CIdx (p = 0.3029, CI–0.833 to 0.628; p = 0.7615, 95%CI–0.787 to 0.587) between the Group 1 and 2 respective and controls. Similarly there was no significant difference between the groups and controls in delta standing CO (p = 0.2251, 95%CI–0.565 to 2.129; p = 0.6137, 95%CI–1.505 to 0.917) and CIdx (p = 0.4658, 95%CI–0.364 to 1.146; p = 0.6349, 95%CI–0.886 to 0.557).Conclusions: There is no evidence of differences in maternal cardiovascular adaptation in relation to pregnancy viability at 6 weeks in women with pregnancies of unknown viability or those destined to miscarry compared to healthy pregnancies. Changes in maternal cardiac output may be related more to the presence of trophoblast than to a viable embryo.

Decreased arterial PO2, not O2 content, increases blood flow through intrapulmonary arteriovenous anastomoses at rest.

The mechanism(s) that regulate hypoxia-induced blood flow through intrapulmonary arteriovenous anastomoses (QIPAVA ) are currently unknown. Our previous work has demonstrated that the mechanism of hypoxia-induced QIPAVA is not simply increased cardiac output, pulmonary artery systolic pressure or sympathetic nervous system activity and, instead, it may be a result of hypoxaemia directly. To determine whether it is reduced arterial PO2 (PaO2) or O2 content (CaO2) that causes hypoxia-induced QIPAVA , individuals were instructed to breathe room air and three levels of hypoxic gas at rest before (control) and after CaO2 was reduced by 10% by lowering the haemoglobin concentration (isovolaemic haemodilution; Low [Hb]). QIPAVA , assessed by transthoracic saline contrast echocardiography, significantly increased as PaO2 decreased and, despite reduced CaO2 (via isovolaemic haemodilution), was similar at iso-PaO2. These data suggest that, with alveolar hypoxia, low PaO2 causes the hypoxia-induced increase in QIPAVA , although where and how this is detected remains unknown. Alveolar hypoxia causes increased blood flow through intrapulmonary arteriovenous anastomoses (QIPAVA ) in healthy humans at rest. However, it is unknown whether the stimulus regulating hypoxia-induced QIPAVA is decreased arterial PO2 (PaO2) or O2 content (CaO2). CaO2 is known to regulate blood flow in the systemic circulation and it is suggested that IPAVA may be regulated similar to the systemic vasculature. Thus, we hypothesized that reduced CaO2 would be the stimulus for hypoxia-induced QIPAVA . Blood volume (BV) was measured using the optimized carbon monoxide rebreathing method in 10 individuals. Less than 5days later, subjects breathed room air, as well as 18%, 14% and 12.5% O2 , for 30min each, in a randomized order, before (CON) and after isovolaemic haemodilution (10% of BV withdrawn and replaced with an equal volume of 5% human serum albumin-saline mixture) to reduce [Hb] (Low [Hb]). PaO2 was measured at the end of each condition and QIPAVA was assessed using transthoracic saline contrast echocardiography. [Hb] was reduced from 14.2±0.8 to 12.8±0.7gdl(-1) (10±2% reduction) from CON to Low [Hb] conditions. PaO2 was no different between CON and Low [Hb], although CaO2 was 10.4%, 9.2% and 9.8% lower at 18%, 14% and 12.5% O2 , respectively. QIPAVA significantly increased as PaO2 decreased and, despite reduced CaO2, was similar at iso-PaO2. These data suggest that, with alveolar hypoxia, low PaO2 causes the hypoxia-induced increase in QIPAVA . Whether the low PO2 is detected at the carotid body, airway and/or the vasculature remains unknown.

Four-day Head-down Tilt Bed Rest as a Model for Studying Rapid Alterations in Hemoglobin Mass

Rapid decreases in hemoglobin mass (Hbmass) have been reported in healthy humans with spaceflight and following descent from high altitude. It has been proposed that a selective increase in the destruction of young red blood cells (RBCs) mediates these decreases but conclusive evidence demonstrating neocytolysis is lacking. Based on the proposed triggers and time course of adaptation during spaceflight, we hypothesized that 4 days of −6° head-down tilt bed rest (HDTBR) would cause a rapid decrease in Hbmass that would be associated with evidence of increased RBC destruction. PURPOSE: To examine changes in Hbmass before (PRE), 5 hours after (POST), and 5 days after (POST5) 4 days of HDTBR. METHODS: Seven healthy, recreationally active men (age: 21 ± 3 years, peak oxygen uptake: 50 ± 6 mL kg-1 min-1) completed 4 days of HDTBR. Hbmass was assessed using the optimized carbon monoxide rebreathing method. Markers of RBC production and destruction assessed included [erythropoietin] ([EPO]), [soluble transferrin receptor] ([sTfr]), reticulocyte count, [ferritin], [haptoglobin], and [bilirubin]. RESULTS: [EPO] decreased by 30 ± 33% from PRE to POST (p = 0.028). Contrary to our hypothesis, Hbmass was increased by 4.0 ± 4.3% from PRE to POST (p = 0.014) before decreasing to a level 3.6 ± 2.4% below PRE at POST5 (p = 0.027). From PRE to POST, [haptoglobin] increased 66 ± 73% (p = 0.013), [bilirubin] decreased 26 ± 34% (p = 0.054), [ferritin] increased 17 ± 17 % (p = 0.012), and reticulocyte count remained stable. From PRE to POST5, sTfr decreased 17 ± 5% (p = 0.018) but there were no significant alterations in [ferritin], [haptoglobin], [bilirubin] or reticulocyte count. CONCLUSION: Our findings suggest that 4-day HDTBR results in a transient increase in Hbmass that may be influenced by decreased RBC destruction. However, since the POST measurement occurred following re-ambulation, a potential role for other factors (i.e., spleen contraction) on the increase in Hbmass cannot be excluded. The decrease in Hbmass at POST5 appears to be mediated by decreased RBC production rather than increased RBC destruction. These findings highlight the need to re-examine the time course and mechanisms of Hbmass alterations with short-term spaceflight and simulated microgravity.

Noninvasive measurement of cardiac output during 6-minute walk test by inert gas rebreathing to evaluate heart failure

Objective The objective of this study was to assess the clinical value of cardiac output (CO) measurements using the inert gas rebreathing (IGR) method during the 6-minute walk test (6MWT) in evaluation of chronic heart failure (CHF).Methods and results A total of 56 CHF patients in our hospital who conformed to the Framingham CHF diagnostic criteria were recruited to this study from October 2007 to February 2009. Subjects were asked to complete a 6MWT and a bicycle exercise test. The CO was measured during both tests using IGR. B-type natriuretic peptide (BNP) levels and the left ventricular ejection fraction (LVEF) were measured at rest. The 6MWT did not correlate with BNP, LVEF, peak cardiac output (PCO), or CO during the 6MWT (CO6MWT). A negative correlation between CO6MWT and BNP as well as a strong correlation between CO6MWT and PCO was observed. When atrial fibrillation and valvular heart disease patients were excluded, CO6MWT and LVEF became significantly correlated. After grouping patients into tertiles according to their PCO values, the PCO remained correlated with CO6MWT within each group. The mean difference between CO6MWT and PCO decreased with decreases in the mean PCO in each group. No significant differences were found in the third tertile (PCO < 10.1 L/min).Conclusions The IGR method during 6MWT is safe and reliable to evaluate cardiac function in patients with CHF.

The Prognostic Value of Peak Cardiac Power Output in Chinese Patients with Chronic Heart Failure.

BackgroundCardiopulmonary exercise testing has been widely used to risk stratify patients with chronic heart failure (CHF). Peak oxygen consumption (peakVO2) was regarded as a powerful predictor of survival, as it is a surrogate for peak cardiac output (CO), which by most is considered the “true” measure of heart failure. Therefore, it is reasonable to hypothesize that CO is an even stronger predictor than peak VO2. The present study is aimed to investigate the prognostic value of peak cardiac power output (peak CPO) in comparison with peakVO2 in Chinese patients with CHF.MethodsParticipants provided written informed consent to participate in this study. Totally 129 patients with CHF underwent symptom-limited cardiopulmonary exercise testing (CPET), with mean age 59.1±11.4 years, 87.6% male, 57.4% ischemic etiology, body mass index (BMI) 24.7±3.7 kg/m2 and LVEF 38±9%. CO was measured using an inert gas rebreathing method. The primary endpoints are cardiac deaths.ResultsOver median 33.7-month follow-up, 19 cardiac deaths were reported. Among peak VO2,VE/VCO2 slope and Peak CPO, their area under ROC were 0.64, 0.67, 0.68, respectively (Ρ<0.05).The optimal thresholds for predicting cardiac deaths were peak VO2≤13.4 ml.kg-1.min-1, and VE/VCO2 slope≥39.3 and peak CPO≤ 1.1 respectively by ROC analysis. Finally, in patients with a peak VO2≤13.4 ml.kg-1.min-1 those with peak CPO>1.1W had better survival than those with peak CPO ≤ 1.1W. However, by multivariate analysis adjusted for age, sex, BMI, resting heart rate, LVMI, LVEF, Peak CPO was not an independent predictor of cardiac deaths (P> 0.05).ConclusionsPeak CPO was not a predictor of cardiac death in Chinese CHF patients.

Closed circuit rebreathing to achieve inert gas wash-in for multiple breath wash-out.

Multiple breath wash-out (MBW) testing requires prior wash-in of inert tracer gas. Wash-in efficiency can be enhanced by a rebreathing tracer in a closed circuit. Previous attempts to deploy this did not account for the impact of CO2 accumulation on patients and were unsuccessful. We hypothesised that an effective rebreathe wash-in could be delivered and it would not alter wash-out parameters.Computer modelling was used to assess the impact of the rebreathe method on wash-in efficiency. Clinical testing of open and closed circuit wash-in–wash-out was performed in healthy controls and adult patients with cystic fibrosis (CF) using a circuit with an effective CO2 scrubber and a refined wash-in protocol.Wash-in efficiency was enhanced by rebreathing. There was no difference in mean lung clearance index between the two wash-in methods for controls (6.5 versus 6.4; p=0.2, n=12) or patients with CF (10.9 versus 10.8; p=0.2, n=19). Test time was reduced by rebreathe wash-in (156 versus 230 s for CF patients, p<0.001) and both methods were well tolerated. End wash-in CO2 was maintained below 2% in most cases.Rebreathe–wash-in is a promising development that, when correctly deployed, reduces wash-in time and facilitates portable MBW testing. For mild CF, wash-out outcomes are equivalent to an open circuit.

Progressive, High Intensity Endurance Exercise Training Significantly Increases Submaximal and Maximal Stroke Volume In Middle Aged, Previously Sedentary Adults

High intensity, endurance exercise increases maximal stroke volume (SV) in young, healthy adults. It is less clear whether such gains are realized among sedentary adults who begin such a program during middle-age. PURPOSE: To determine whether a progressive, high-intensity endurance exercise program will increase SV in healthy, middle-aged adults. METHODS: We studied 42 middle-aged adults (18 males; 52.1 ± 5.0yrs). 21 were randomized to a non-aerobic exercise group (Control). The remaining 21 (10 males) were assigned to an endurance training group (Exercise), all whom completed the 9-month progression phase of a 24 month exercise prescription. This progressive regimen was gradually expanded from 3*30min moderate intensity sess./wk to 1-2*30 min and 1*60 min moderate intensity (55-70% of VO2max) sess./wk + 2 high intensity interval (≥95%peakHR) sess./wk; and 1 low intensity recovery sess./wk. Endurance training sessions were recorded by each participant via both Polar heart rate monitoring and manual data logs. VO2max was measured using the Douglas Bag method via an incremental treadmill protocol. Cardiac output (Qc) was measured by a non-invasive acetylene rebreathing method. VO2 and Qc were measured at rest, two submaximal (SS1 and SS2, 30 and 60% of peak VO2, respectively) and maximal workloads. SV was calculated from the Qc and HR measured via ECG. RESULTS: Exercise participants increased their SV at the submaximal (10.2 and 11.6%, respectively; both p<0.01) and maximal (9.7%, p=0.02) workloads (reference Table 1). SV of the Control group decreased slightly at all workloads. CONCLUSION: Healthy, previously sedentary middle-aged adults who completed a progressive endurance exercise program realized a significant increase in SV during both submaximal and maximal exercise.Table 1: Stroke Volume Increases with Progressive Endurance Training

Decreased Arterial PO 2 , not O 2 Content, Increases Blood Flow Through Intrapulmonary Arteriovenous Anastomoses at Rest

Alveolar hypoxia, not increased pulmonary artery pressure, causes increased blood flow through intrapulmonary arteriovenous anastomoses (QIPAVA) in humans. However, it is unknown whether the hypoxic stimulus for QIPAVA is decreased arterial PO2 (PaO2) or arterial O2 content (CaO2). CaO2 is known to regulate blood flow in the systemic circulation and it is suggested that QIPAVA is regulated similar to the systemic vasculature. Thus, we hypothesized that reduced CaO2 would be the stimulus for hypoxia-induced QIPAVA. Blood volume (BV) was measured using the optimized carbon monoxide rebreathing method in 8 healthy subjects, 1 female. Less than 5 days later subjects breathed 18%, 14%, and 12.5% O2 for 30 min each, in a randomized order, before and after isovolemic hemodilution (IH; 10% of BV withdrawn and replaced with an equal volume of 5% human serum albumin). PaO2 was obtained at the end of each trial and QIPAVA was assessed using saline contrast echocardiography. Hemoglobin concentration was reduced from 14.2 ± 0.7 to 12.8 ± 0.5 g/dL with IH. PaO2 did not change pre- and post-IH at any FIO2, but CaO2 was 10.1, 11.3, and 5.4% lower at 18, 14, and 12.5% O2, respectively. QIPAVA was significantly increased as PaO2 decreased and despite reduced CaO2, was similar at iso-PO2. These data suggest that with alveolar hypoxia, low PaO2 causes the hypoxia-induced increase in QIPAVA. Support: Department of Defense

Replicate Measurements of Haemoglobin Mass during a Single Day are Feasible and Precise.

Duplicate haemoglobin mass (Hbmass) measurements are recommended before and after altitude training sojourns to identify individual adaptations in athletes with a high level of certainty. Duplicate measurements reduce typical error (TE) and disclose measurement outliers, but are usually made on separate days, which is not a practical protocol for routine services in elite sport settings. The aim of this study was therefore to investigate whether it is safe (carboxyhaemoglobin<10%) to measure Hbmass twice on the same day and to compare TE with measurements made on separate days. 18 healthy men completed 3 different procedures to measure Hbmass twice a day with the carbon monoxide rebreathing method: A (Hbmass measured twice within 6 h), B (dito A, combined with 1 h of hyperoxic training between the tests), C (dito B, within 2 h). First Hbmass measurements of the 3 test days served as procedure D. Carboxyhaemoglobin did not exceed 10% in any procedure. TE and confidence limits for procedures A, B, C and D were 1.4% (1.0-2.1%), 1.1% (0.8-1.7%), 1.3% (1.0-2.0%) and 1.5% (1.2-2.1%), respectively. Duplicate measurements of Hbmass on the same day are feasible and show TE similar to triplicate measurements on separate days.

Central and peripheral cardiovascular impairments limit VO(2peak) in type 1 diabetes.

Cardiovascular risk, predicted by peak O2 uptake (VO(2peak)), is increased in type 1 diabetes. We examined the contribution of central and peripheral mechanisms to VO(2peak) in physically active adults with type 1 diabetes. Seven men with type 1 diabetes and 10 healthy age-, anthropometry-, and physical activity-matched men performed incremental cycling exercise until volitional fatigue. Alveolar gas exchange (turbine and mass spectrometry), cardiac function and systemic vascular resistance (impedance cardiography), and local active leg muscle deoxygenation and blood flow (near infrared spectroscopy) were monitored. Arterial-venous O2 difference was calculated (Fick principle). Blood volume (BV) (carbon monoxide rebreathing method) and glycemic control (glycosylated hemoglobin) were determined. The group with diabetes had lower VO(2peak) than controls (47 ± 5 vs 56 ± 7 mL·min·kg fat-free mass, P < 0.05). At peak exercise, fat-free mass-adjusted stroke volume (SV) and cardiac output (CO) were lower and systemic vascular resistance was higher in the group with diabetes than those in controls (P < 0.05). Leg muscle blood flow was reduced independently of CO in the group with diabetes at peak exercise (P < 0.05), whereas arterial-venous O2 difference was similar in the groups throughout the exercise (P > 0.05). The group with diabetes had lower relative BV than controls (P < 0.01), and BV correlated positively with peak SV and peak CO (P < 0.001). In the group with diabetes, peak SV and peak CO correlated (P < 0.05) and peak leg muscle blood flow tended to correlate (P = 0.070) inversely with glycosylated hemoglobin. Both central and peripheral cardiovascular impairments limit VO(2peak) in physically active adults with type 1 diabetes. Importantly, central limitations, and probably peripheral limitations as well, are associated with glycemic control.

Modulation of Ventilatory Reflex Control by Cardiac Resynchronization Therapy

BackgroundHeart failure (HF) is characterized by heightened sensitivities of the CO2 chemoreflex and the ergoreflex which promote increased ventilatory drive manifested as increased minute ventilation per volume of expired CO2 (VE/VCO2). The aims of this study were to evaluate the effects of cardiac resynchronization therapy (CRT) on carbon dioxide (CO2) chemosensitivity and the arterial CO2 setpoint. Methods and ResultsConsecutive HF patients (n = 35) who underwent clinically indicated CRT were investigated by means of cardiopulmonary exercise testing and CO2 chemosensitivity evaluation with the use of a rebreathe method before and 4-6 months after CRT. Pre- and post-CRT measures were compared with the use of either paired t test or Wilcoxon test. Decreased peak VE/VCO2 (44 ± 10 vs 40 ± 8; P < .01), CO2 chemosensitivity (2.2 ± 1.1 vs 1.7 ± 0.8 L min−1 mm Hg−1; P = .04), and increased peak end-tidal CO2 (29 ± 5 vs 31 ± 5 mm Hg; P < .01) were also observed after CRT. Multivariate analysis adjusted for age and sex showed the decrease of peak VE/VCO2 from before to after CRT to be most strongly associated with the increase of peak end-tidal CO2 (β = −0.84; F = 21.5; P < .0001). ConclusionsDecrease of VE/VCO2 after CRT is associated with decreased CO2 chemosensitivity and increase of the arterial CO2 setpoint, which is consistent with decreased activation of both the CO2 chemoreflex and the ergoreflex.

Management of post-hyperventilation apnea during dental treatment under monitored anesthesia care with propofol.

Although hyperventilation syndrome generally carries a good prognosis, it is associated with the risk of developing severe symptoms, such as post-hyperventilation apnea with hypoxemia and loss of consciousness. We experienced a patient who suffered from post-hyperventilation apnea. A 17-year-old female who suffered from hyperventilation syndrome for several years developed post-hyperventilation apnea after treatment using the paper bag rebreathing method and sedative administration during a dental procedure. We subsequently successfully provided her with monitored anesthesia care with propofol. Monitored anesthesia care with propofol may be effective for the general management of patients who have severe hyperventilation attacks and post-hyperventilation apnea. This case demonstrates that appropriate emergency treatment should be available for patients with hyperventilation attacks who are at risk of developing post-hyperventilation apnea associated with hypoxemia and loss of consciousness.

Comparison of total haemoglobin mass measured with the optimized carbon monoxide rebreathing method across different Radiometer™ ABL-80 and OSM-3 hemoximeters

A new Radiometer™ hemoximeter (ABL-80) has recently become available to measure carboxyhaemoglobin concentration for the optimized CO-rebreathing method (oCOR-method). Within the English Institute of Sport (EIS), hemoximeters are used in three different laboratories; therefore, precision and agreement of total haemoglobin mass (tHbmass) determination across sites is essential, and comparison to the previous model OSM-3 is desirable. Six male and one female (age 30 ± 6 years, body mass 78.1 ± 10.6 kg) undertook the oCOR-method. Venous blood (~2 ml) was sampled immediately before and at 7 min during the oCOR-method; with seven replicates from each time point simultaneously analysed on five different Radiometer™ hemoximeters [OSM-3(1), OSM-3(2), ABL-80(1), ABL-80(2) and ABL-80(3)]. There were no differences (p > 0.05) between Δ%HbCO or mean tHbmass analysed with five different hemoximeters (OSM-3(1): 886 ± 167 g; OSM-3(2): 896 ± 160 g: ABL-80(1): 904 ± 157 g; ABL-80(2): 906 ± 163 g: ABL-80(3): 906 ± 162 g). However, the Bland–Altman plot revealed that there was closer agreement between ABL-80 machines for tHbmass than for the OSM-3. The variance (i.e. % error) across replicate samples decreased as the number of samples increased, with the error derived from the ‘worse-case’ scenario (single samples) being 1.2 to 1.6 fold greater in the OSM-3 than the ABL-80. Although there were no differences in the average tHbmass measured with five different hemoximeters, the new ABL-80 were in better agreement with each other compared to the old OSM-3. Previously, five replicates were required to achieve a low error using the OSM-3; however, three replicates are sufficient with the ABL-80 model to produce an error of ≤ 1% in tHbmass.

Shorter intervals at peak SV vs.V̇O2max may yield high SV with less physiological stress

The purpose of this study was to evaluate whether greater and sustainable stroke volume (SV) responses may be obtained by exercise intensities corresponding to peak SV (SVpeak) vs. maximal O2 consumption (), and short vs. long intervals (SI vs. LI). Nine moderate- to well-trained male athletes competing at regional level specialists of cyclist, track and field volunteered to take part in the study (: 59.7 ± 7.4 mL·min−1·kg−1). Following familiarisation sessions, was determined, and then SVpeak was evaluated using exercise intensities at 40%–100% of by nitrous-oxide rebreathing (N2ORB) method. Then each separate participant exercised wattages corresponding to individual and SVpeak during both SI (SI and SISVpeak) and LI (LI and LISVpeak) workouts on a cycle ergometer. Main results showed that both SI and SISVpeak yielded greater SV responses than LI and LISVpeak (p ≤ 0.05). Mean SV responses were greater in LISVpeak than in LI (p ≤ 0.05), but there was no statistical difference between SISVpeak and SI. However, there was significantly less physiological stress based on VO2, respiratory exchange ratio, heart rate and rate of perceived exhaustion in SVpeak than in intensities (p ≤ 0.05). Moreover, SV responses at exercise phases increased in the early stages and remain stable until the end of SI and SISVpeak workouts (p > 0.05), while they were gradually decreasing in LI and LISVpeak sessions (p ≤ 0.05). In conclusion, if the aim of a training session is to improve SVpeak with less physiological stress, SISVpeak seems a better alternative than other modalities tested in the present study.

The effect of a period of intense exercise on the marker approach to detect growth hormone doping in sports.

The major objective of this study was to investigate the effects of several days of intense exercise on the growth hormone marker approach to detect doping with human growth hormone (hGH). In addition we investigated the effect of changes in plasma volume on the test. Fifteen male athletes performed a simulated nine-day cycling stage race. Blood samples were collected twice daily over a period of 15 days (stage race + three days before and after). Plasma volumes were estimated by the optimized CO Rebreathing method. IGF-1 and P-III-NP were analyzed by Siemens Immulite and Cisbio Assays, respectively. All measured GH 2000 scores were far below the published decision limits for an adverse analytical finding. The period of exercise did not increase the GH-scores; however the accompanying effect of the increase in Plasma Volume yielded in essentially lower GH-scores. We could demonstrate that a period of heavy, long-term exercise with changes in plasma volume does not interfere with the decision limits for an adverse analytical finding.

NO ASSOCIATION BETWEEN tHbmass AND POLYMORPHISMS IN THE HBB GENE IN ENDURANCE ATHLETES.

The aim of this study was to examine the association between tHbmass and HBB gene polymorphisms in athletes of endurance disciplines. Eighty-two well-trained athletes (female n=36, male n=46), aged 19.3 ± 2.7 years, representing cross country skiing (n=37) and middle- and long-distance running (n=45), participated in the study. Genotyping for 2 polymorphisms in the HBB gene (- 551C/T and intron 2, +16 C/G) was performed using restriction fragment length polymorphism analysis. Total haemoglobin mass (tHbmass) was determined by the optimized carbon monoxide rebreathing method. Blood morphology, indices of iron status (ferritin, transferrin receptor and total iron binding capacity) and C reactive protein were also determined. No differences were found in the HBB genotype and allele frequencies between male and female athletes. Regardless of the polymorphisms, no relationships were found between HBB genotypes as well as alleles and relative values of tHbmass, expressed per body mass (g · kg-1 BM), both in female and male athletes. Our results demonstrated that -551 C/T and intron 2, +16 C/G polymorphisms of the HBB gene have no association with total haemoglobin mass in endurance athletes. It cannot be ruled out that several polymorphisms, each with a small but significant contribution, may be responsible for the amount of haemoglobin.

Management of post-hyperventilation apnea during dental treatment under monitored anesthesia care with propofol

Although hyperventilation syndrome generally carries a good prognosis, it is associated with the risk of developing severe symptoms, such as post-hyperventilation apnea with hypoxemia and loss of consciousness. We experienced a patient who suffered from post-hyperventilation apnea. A 17-year-old female who suffered from hyperventilation syndrome for several years developed post-hyperventilation apnea after treatment using the paper bag rebreathing method and sedative administration during a dental procedure. We subsequently successfully provided her with monitored anesthesia care with propofol. Monitored anesthesia care with propofol may be effective for the general management of patients who have severe hyperventilation attacks and post-hyperventilation apnea. This case demonstrates that appropriate emergency treatment should be available for patients with hyperventilation attacks who are at risk of developing post-hyperventilation apnea associated with hypoxemia and loss of consciousness.

AltitudeOmics: enhanced cerebrovascular reactivity and ventilatory response to CO2 with high-altitude acclimatization and reexposure

The present study is the first to examine the effect of high-altitude acclimatization and reexposure on the responses of cerebral blood flow and ventilation to CO2. We also compared the steady-state estimates of these parameters during acclimatization with the modified rebreathing method. We assessed changes in steady-state responses of middle cerebral artery velocity (MCAv), cerebrovascular conductance index (CVCi), and ventilation (V(E)) to varied levels of CO2 in 21 lowlanders (9 women; 21 ± 1 years of age) at sea level (SL), during initial exposure to 5,260 m (ALT1), after 16 days of acclimatization (ALT16), and upon reexposure to altitude following either 7 (POST7) or 21 days (POST21) at low altitude (1,525 m). In the nonacclimatized state (ALT1), MCAv and V(E) responses to CO2 were elevated compared with those at SL (by 79 ± 75% and 14.8 ± 12.3 l/min, respectively; P = 0.004 and P = 0.011). Acclimatization at ALT16 further elevated both MCAv and Ve responses to CO2 compared with ALT1 (by 89 ± 70% and 48.3 ± 32.0 l/min, respectively; P < 0.001). The acclimatization gained for V(E) responses to CO2 at ALT16 was retained by 38% upon reexposure to altitude at POST7 (P = 0.004 vs. ALT1), whereas no retention was observed for the MCAv responses (P > 0.05). We found good agreement between steady-state and modified rebreathing estimates of MCAv and V(E) responses to CO2 across all three time points (P < 0.001, pooled data). Regardless of the method of assessment, altitude acclimatization elevates both the cerebrovascular and ventilatory responsiveness to CO2. Our data further demonstrate that this enhanced ventilatory CO2 response is partly retained after 7 days at low altitude.

CO2 rebreathing: an undergraduate laboratory to study the chemical control of breathing

The Read CO2 rebreathing method (Read DJ. A clinical method for assessing the ventilatory response to carbon dioxide. Australas Ann Med 16: 20-32, 1967) provides a simple and reproducible approach for studying the chemical control of breathing. It has been widely used since the modifications made by Duffin and coworkers. Our use of a rebreathing laboratory to challenge undergraduate science students to investigate the control of breathing provided 8 yr of student-generated data for comparison with the literature. Students (age: 19-22 yr, Research Ethics Board approval) rebreathed from a bag containing 5% CO2 and 95% O2 (to suppress the peripheral chemoreflex to hypoxia). Rebreathing was performed, and ventilation measured, after hyperventilation to deplete tissue CO2 stores and enable the detection of the central chemoreflex threshold. We analyzed 43 data sets, of which 10 were rejected for technical reasons. The mean threshold and ventilatory sensitivity to CO2 were 43.3 ± 3.8 mmHg and 4.60 ± 3.04 l·min(-1)·mmHg(-1) (means ± SD), respectively. Threshold values were normally distributed, whereas sensitivity was skewed to the left. Both mean values agreed well with those in the literature. We conclude that the modified rebreathing protocol is a robust method for undergraduate investigation of the chemical control of breathing.

Altitude training and haemoglobin mass from the optimised carbon monoxide rebreathing method determined by a meta-analysis

ObjectiveTo characterise the time course of changes in haemoglobin mass (Hbmass) in response to altitude exposure.MethodsThis meta-analysis uses raw data from 17 studies that used carbon monoxide rebreathing to determine...