Arterial Blood Gases in Normal Subjects at 2240 Meters Above Sea Level: Impact of Age, Gender, and Body Mass Index.

Background: The values of arterial blood gases (ABG) change with altitude above sea level; empirical verification is essential because ventilatory acclimatization varies with ethnicity and a population's adaptation. Objective: The aim of the study was to describe ABG in a healthy population residing at 2,240 meters above sea level, to identify the mean level of alveolar ventilation (PaCO2), and to know whether a progressive increase in PaCO2 occurs with age and the impact of increasing body mass index (BMI). Methods: We conducted a cross-sectional study in a referral center for respiratory diseases in Mexico City. Associations among variables with correlation coefficient and regression models of PaO2, SaO2, and P(A-a)O2 as dependent variables as a function of age, BMI, minute ventilation, or breathing frequency were explored. Results: Two hundred and seventeen healthy subjects were evaluated with a mean age of 40 ± 15 years, mean of the PaO2 was 71 ± 6 mmHg, SaO2 94% ± 1.6%, PaCO2 30.2 ± 3.4 mmHg, HCO3 20 ± 2 mmol/L, BE-2.9 ± 1.9 mmol/L, and the value of pH was 7.43 ± 0.02. In a linear regression, the main results were PaO2 = 77.5-0.16*age (p < 0.0001) and with aging P(A-a)O2 tended to increase 0.12 mmHg/year. PaCO2 in women increased with age by 0.075 mmHg/year (p = 0.0012, PaCO2 =26.3 + 0.075*age). SaO2 and PaO2 decreased significantly in women with higher BMI 0.14% and 0.52 mmHg per kg/m2, (p = 0.004 and 0.002 respectively). Conclusion: Mean PaCO2 was 30.7 mmHg, implying a mean alveolar ventilation of around 30% above that at sea level.

Comparing Spirometric Reference Values From Childhood to Old Age Estimated by LMS and Linear Regression Models.

BACKGROUND: Proper reference values for lung function testing are essential for achieving adequate interpretations. The LMS procedure (lambda, mu, sigma) permits continuous analyses of entire populations avoiding gaps in the transition between childhood and adulthood. It also allows more precise calculations of average values, dispersion, and 5th percentiles, which are usually considered the lower limit of normality. The objective of this study was to compare our results fitted with the LMS method with standard multiple linear regression, and with those from international Global Lung Function Initiative (GLI) equations. METHODS: Data from 9835 healthy residents of the metropolitan area of Mexico City aged 8-80 years were compiled from several studies: EMPECE, PLATINO, adult Mexican workers and two unpublished studies. The LMS procedure and multiple linear regression models were fit to obtain reference equations using R software. RESULTS: Residuals from the LMS models had a median closer to zero, and smaller dispersion than those from the linear model, but differences although statistically significant were very small and of questionable practical relevance. For example, for females and ln(FEV1), median residual was -0.001 with p25 of -0.08 and p75 of 0.08 for LMS, compared with 0.004 (-0.08, 0.09) [p<0.05] for the linear model. Average spirometric values for a given height for our population, were higher than those predicted by the GLI study. CONCLUSION: Continuous reference equations for the Mexican population calculated using the LMS technique showed slightly better fit than linear regression models.

Shorter corridors can be used for the six-minute walk test in subjects with chronic lung diseases.

BACKGROUND: The main limitation of the six-minute walk test (6-MWT) is that not all pulmonary function testing facilities have an indoor flat, 30-m-long corridor. Therefore, this study aimed 1) to evaluate the correlation and agreement of the distances walked in 30-m- vs. 15-m-long corridors by subjects with chronic lung diseases (CLD group) and 2) to compare the levels of oxygen saturation (nSpO2), blood pressure (BP), heart rate recovery at minute one post-exercise (HRR1), and Borg scale scores for dyspnea and fatigue between the two distances walked. METHODS: A prospective, cross-sectional study was conducted at the National Institute of Respiratory Diseases in Mexico City. Subjects with chronic lung diseases and healthy adults were invited to participate. The distance of the 6-MWT was randomly assigned based on whether the first test was in the 15-m or 30-m corridor. RESULTS: Ninety individuals were included; the correlation in meters walked between the two corridors was r = 0.96 in CLD; the 95% limits of agreement for the 6-MWT ranged from -73 to +37 m. Most subjects walked further in the 30-m corridor (82%); however, the percent predicted values for the CLD group were 3.5% lower for the 15-m corridor than the 30-m corridor. Only 10.5% of the subjects with CLD would have been falsely classified as having a normal 6-MWT (false negative). No significant differences in the nSpO2, Borg scale, BP or HRR1 were found between the two 6-MWT corridor lengths. CONCLUSION: The 6-MWT can be performed using a 15-m corridor in subjects with CLD, and the results for the distance walked, HRR1, nSpO2, and Borg scale scores are similar to between the 15-m and 30-m corridors.

Inspiratory Capacity and Vital Capacity of Healthy Subjects 9-81 Years of Age at Moderate-High Altitude.

BACKGROUND: Measurements of inspiratory capacity (IC) and vital capacity (VC) are used to recognize dynamic hyperinflation, but appropriate reference values are required to achieve accurate clinical interpretations. Altitude above sea level is a potential determining factor for lung volumes, including IC and VC. OBJECTIVE: To describe IC and VC for healthy people who live in Mexico City at an altitude of 2,240 m above sea level. METHODS: Healthy subjects ages 9-81 y completed slow spirometry by following 2005 American Thoracic Society/European Respiratory Society standards. Once associations were explored, linear regression models were constructed and values were compared with those from previously published equations. RESULTS: A total of 441 healthy subjects (55.1% women) participated. The mean age was 32 y (minimum age, 9 y; maximum age, 81 y). IC and VC measurements were associated with sex, age, height, and weight. An accelerated increase in IC and VC was evident from 9 to 20 y of age, followed by a gradual decrease in both sexes. In general, IC was higher in our population than predicted by previously published reference equations. CONCLUSIONS: IC in healthy people at 2,240 m above sea level was higher than that of previous reports about European and Latin-American subjects of the same height, sex, and age who were at sea level. The present study provided robust reference values for persons who lived at a moderate altitude.

Diffusing Capacity of the Lung for Carbon Monoxide in Mexican/Latino Children. Quality Control and Reference Values.

RATIONALE: Single-breath diffusing capacity of the lung for carbon monoxide (DlCOsb) values are used to evaluate gas exchange; however, the quality of maneuvers performed by children has not been evaluated, and reference values for young people living at moderate altitudes are not well established. OBJECTIVES: Our objectives were 1) to determine whether DlCOsb maneuvers performed by a pediatric population would meet 2017 European Respiratory Society/American Thoracic Society (ERS/ATS) quality control standards; and 2) to report normal DlCOsb values for Mexican/Latino children and adolescents living at moderate altitudes. METHODS: This study involved healthy young people 4-20 years of age from the metropolitan area of Mexico City (2,240 m above sea level) who were recruited in schools from July 2014 to August 2017. DlCOsb testing was performed according to the 2005 ATS/ERS standards, and the quality control of each maneuver was analyzed according to the 2017 ERS/ATS standards. We constructed models for DlCOsb with linear and quadratic terms for weight, height, and age as independent variables using shrinkage statistics, variance inflation factors, the Akaike information criterion, and R2 to compare the results of different models. RESULTS: Results were obtained for 420 individuals (53% boys) with a mean age of 11.7 ± 4.5 standard deviation (SD) years; 47% of maneuvers from children age 4-6 years were grade A (13% grade B), and 90% of those in children older than 13 years were grade A or B. Forty-six percent of the subjects had a DlCOsb repeatability of <1 ml/min/mm Hg. The mean DlCOsb was higher for boys than for girls (32.4 ± 13.6 [SD] vs. 24.1 ± 7.5 ml/min/mm Hg, respectively). The reference equation for boys was DlCOsb = exp(1.63469 + [0.03251 × age] + [0.00846 × height] + [0.00304 × weight]), R2 = 0.87; for girls, the best equation was DlCOsb = exp(1.56516 + [0.0193 × age] + [0.00893 × height] + [0.00273 × weight]), R2 = 0.75. The single-breath transfer coefficient of the lung for carbon monoxide remained constant with age and height, with a lower limit of normal of 6.5 ml/min/mm Hg/L in boys and 5.4 ml/min/mm Hg/L in girls. Measured DlCOsb was higher than predicted by other authors (P < 0.001 by paired t test). CONCLUSIONS: Individuals 4-20 years of age can complete high-quality DlCOsb tests. Children and adolescents living at 2,240 m have higher DlCOsb values than those living at sea level. Reference equations for DlCOsb obtained at sea level are poor predictors of the values measured at moderate altitude.

Arterial Blood Gases in Normal Subjects at 2240 Meters Above Sea Level: Impact of Age, Gender, and Body Mass Index

ABSTRACT Background The values of arterial blood gases (ABG) change with altitude above sea level; empirical verification is essential because ventilatory acclimatization varies with ethnicity and a population's adaptation. Objective The aim of the study was to describe ABG in a healthy population residing at 2,240 meters above sea level, to identify the mean level of alveolar ventilation (PaCO2), and to know whether a progressive increase in PaCO2 occurs with age and the impact of increasing body mass index (BMI). Methods We conducted a cross-sectional study in a referral center for respiratory diseases in Mexico City. Associations among variables with correlation coefficient and regression models of PaO2, SaO2, and P(A-a)O2 as dependent variables as a function of age, BMI, minute ventilation, or breathing frequency were explored. Results Two hundred and seventeen healthy subjects were evaluated with a mean age of 40 ± 15 years, mean of the PaO2 was 71 ± 6 mmHg, SaO2 94% ± 1.6%, PaCO2 30.2 ± 3.4 mmHg, HCO3 20 ± 2 mmol/L, BE-2.9 ± 1.9 mmol/L, and the value of pH was 7.43 ± 0.02. In a linear regression, the main results were PaO2 = 77.5-0.16*age (p < 0.0001) and with aging P(A-a)O2 tended to increase 0.12 mmHg/year. PaCO2 in women increased with age by 0.075 mmHg/year (p = 0.0012, PaCO2 =26.3 + 0.075*age). SaO2 and PaO2 decreased significantly in women with higher BMI 0.14% and 0.52 mmHg per kg/m2, (p = 0.004 and 0.002 respectively). Conclusion Mean PaCO2 was 30.7 mmHg, implying a mean alveolar ventilation of around 30% above that at sea level.

Validating Reference Equations for Impulse Oscillometry in Healthy Mexican Children.

BACKGROUND: The impulse oscillometry system (IOS) measures the impedance (Z) of the respiratory system, but proper interpretation of its results requires adequate reference values. The objectives of this work were: (1) to validate the reference equations for the IOS published previously by our group and (2) to compare the adjustment of new available reference equations for the IOS from different countries in a sample of healthy children. METHODS: Subjects were healthy 4-15-y-old children from the metropolitan area of Mexico City, who performed an IOS test. The functional IOS parameters obtained were compared with the predicted values from 12 reference equations determined in studies of different ethnic groups. The validation methods applied were: analysis of the differences between measured and predicted values for each reference equation; correlation and concordance coefficients; adjustment by Z-score values; percentage of predicted value; and the percentage of patients below the lower limit of normality or above the upper limit of normality. RESULTS: Of the 224 participants, 117 (52.3%) were girls, and the mean age was 8.6 ± 2.3 y. The equations that showed the best adjustment for the different parameters were those from the studies by Nowowiejska et al (2008) and Gochicoa et al (2015). The equations proposed by Frei et al (2005), Hellinckx et al (1998), Kalhoff et al (2011), Klug and Bisgaard (1998), de Assumpção et al (2016), and Dencker et al (2006) overestimated the airway resistance of the children in our sample, whereas the equation of Amra et al (2008) underestimated it. In the analysis of the lower and upper limits of normality, Gochicoa et al equation was the closest, since 5% of subjects were below or above percentiles 5 and 95, respectively. The study found that, in general, all of the equations showed greater error at the extremes of the age distribution. CONCLUSIONS: Because of the robust adjustment of the present study reference equations for the IOS, it can be recommended for both clinical and research purposes in our population. The differential adjustment of other equations underlines the need to obtain local reference values.

Long-Term Stability of a Portable Carbon Monoxide Single-Breath Diffusing Capacity Instrument.

BACKGROUND: The 2005 American Thoracic Society/European Respiratory Society guidelines for single-breath diffusing capacity of the lung for carbon monoxide (DLCO) recommend a weekly biological control test and/or DLCO simulator to detect instrument error drift. Very little has been published regarding the results of such a quality assurance program. Our aim was to analyze the long-term stability of a portable DLCO instrument. METHODS: We used a new EasyOne Pro system and checked its accuracy using a DLCO simulator with 2 reference gases (concentration A: carbon monoxide [CO] = 0.1% and helium = 6.52%; concentration B: CO = 0.08% and helium = 7.21%) during the first 3 y of use in our large clinical laboratory. To detect instrument drift, a healthy woman (MSC), age 43 y old at baseline, tested herself every week during this period of time. RESULTS: More than 6,000 spirometry and 5,000 DLCO maneuvers were done using this instrument for patients during these 3 y. There were no failures in the daily volume and flow checks or the CO and helium calibration checks performed automatically by the instrument. The differences between the simulator DLCO and the measured DLCO were -0.91 ± 1.33 mL/min/mm Hg and -0.61 ± 1.45 mL/min/mm Hg for concentration A and concentration B, respectively. The results of the 110 biological control tests were: mean 30.8 ± 1.7 mL/min/mm Hg (95% CI 30.5-31.1), coefficient of variation of 5.4% in DLCO, and repeatability of 2.5 mL/min/mm Hg. Only 4 measurements were outside ±3 mL/min/mm Hg (3.6%). Her mean alveolar volume was 4.2 ± 0.25 L with coefficient of variation of 6.2%; her inspired volume was 3.05 ± 0.14 L, and coefficient of variation = 4.5%. CONCLUSIONS: Measurements of DLCO were stable over the 3-y period without any need for manual recalibration of the instrument. The biological control was as good as the DLCO simulator to evaluate this kind of device in a long-term laboratory quality control program.

Maximum Voluntary Ventilation in a Population Residing at 2,240 Meters Above Sea Level.

BACKGROUND: Measured maximum voluntary ventilation (MVV) correlates with maximum ventilatory capacity during exercise. As a shortcut, MVV is often estimated by multiplying measured FEV1 times 35 or 40, but this index varies with altitude due to reduced air density. The objective was to describe MVV in healthy individuals residing at 2,240 m above sea level and compare it with the reference values customarily employed. METHODS: We recruited a convenience sample of respiratory-healthy, non-obese volunteers >10 y of age who had resided for >2 y in Mexico City. All participants performed forced spirometry and MVV according to current standards. Multiple regression models were fitted, including age, height, and measured FEV1, separately for males and females to obtain reference values. The impact of lower air density on MVV at this elevation was estimated from the reported increase in peak flow in relation to altitude. RESULTS: We studied 381 individuals (210 females [55.1%]) age 10-80 y with a mean MVV of 145.6 ± 48 L/min. Both FEV1 × 35 and FEV1 × 40 underestimated the MVV observed: in males by approximately 26% and in females by approximately 10%. MVV for our population approached FEV1 × 45 (98 ± 15.6% of real MVV). Multiple regression models including height, weight, and measured FEV1 explained 70% of residual variability once sex was taken into account. CONCLUSIONS: At an altitude of 2,240 m, MVV is about 45 times the measured FEV1, and it can be estimated for other altitudes. The best predicting equations for MVV were calculated separately for females and males and included the following predictors: age, age2, and measured FEV1. The study found that reference values for MVV from studies conducted at sea level are inaccurate at this altitude.

[Frequency of NAFLD in a group of patients with metabolic syndrome in Veracruz, Mexico]. / Frecuencia del hígado graso no alcohólico en un grupo de pacientes con sindrome metabólico estudiado en la ciudad de veracruz.

INTRODUCTION: Nonalcoholic fatty liver disease is a very common disease that is being described principally in obese, diabetic and hiperlipidemic patients without significant alcohol consumption (less than 28 ethanol Units per week). Nowadays it is considered as the hepatic manifestation of the metabolic syndrome. The frequency of Non Alcoholic Sreatohepatic (NASH) is 30 to 35% in general population, but it reaches to 70% in patients whose Body Mass Index (BMI) is above 30 kg/m2 as it occurs with diabetic patients. In Mexico there are only isolated reports about it's frequency, nearly 7.1% in general population and 18.5% in diabetic patients. OBJECTIVE: To know the frequency of the Nonalcoholic fatty liver disease in patients who receive medical attention at the city of Veracruz. MATERIAL AND METHODS: We studied 337 patients, who were divided into 4 groups: Normal Weight, Overweight, Obese and Diabetes type 2 patients. The individuals who reported previous hepatitis and alcohol consumption were excluded. All patients made a test in order to determinate: age, gender, presence of hepatic stigmata and complaints. Laboratory tests were done to all patients including: Blood glucose, seric lipids, transaminases, proteins and alkaline phosphatase. In those cases with impairment in transaminases results, it was done upper abdominal ultrasound (USG) and hepatic biopsy, in patients who accepted. RESULTS: We identified 53 cases (15.72%) with characteristics of Nonalcoholic fatty liver disease. The frequency in patient with normal weight and overweight was 7.14% to 7.76%, while in obese subjects it was 14.15% and 28% in diabetic patients; 73.58% of all patients were female and the other 28.41% were males. The average age of the group was 48.11 years, it was similar the specific age of the normal weight and obese patients, in overweight patients was 61.5 years and the average age in diabetics was 56.42 years. There were significant differences in the results of blood glucose level, glycosilated hemoglobin, cholesterol, seric lipid values and aminotransferases in obese and diabetic patients compared with normal subjects and overweight patients in our study, the USG did not show sensibility and specificity to detect Non alcoholic fatty liver disease (NAFLD). DISCUSSION: The results of this study show a lower frequency compared with the rest of the world, however it was higher in diabetic population than the frequency published by Bernal in Hidalgo, Mexico. The aminotransferases level resulted elevated in all patients with metabolic syndrome and NAFLD so we consider that elevated aminotransferases levels is the best predictor to suspect the presence of NAFLD. That is why it's very important to consider the possibility to avoid the progression to cirrhosis and hepatocarcinoma.

[Frequency and clinical, biochemical and histological characteristics of nonalcoholic fatty liver disease in patients with gallstone disease]. / Frecuencia y características clínicas, bioquímicas e histológicas del hígado graso no alcohólico en pacientes con enfermedad litiásica vesicular.

BACKGROUND: In 1980, nonalcoholic fatty liver disease (NALFD) was described. It is related to the genesis of gallstones and is considered as a manifestation of the metabolic syndrome. In order to determine the frequency, anatomoclinical characteristics and biochemical and histological alterations in NAFLD, patients underwent cholecystectomy (GD). For this reason, we considered carrying out this study. METHODS: This was a prospective and observational study. The study population was comprised of patients with gallstone disease who were treated at the "Hospital Español" in Veracruz, Mexico from January 1, 2005 to November 30, 2006 and underwent cholecystectomy and liver biopsy. Analyzed variables were anthropometric characteristics and risk factors, and in each patient biochemical tests, abdominal ultrasound (US) and histological liver study were performed. RESULTS: In 95 patients, according to liver biopsy diagnoses, we found a frequency of 54.74% of NAFLD associated with gallstones. Females were more affected (71.15%) and the average age was 55.6 +/- 17.87 years. Risk factors were obesity (67.3%), diabetes mellitus (17.3%), and dyslipidemia (76.92%). Patients with NAFLD had elevated levels of glucose, glycosylated hemoglobin, cholesterol, triglycerides and HDLcholesterol, and aminotransferases. Abdominal US did not show sufficient specificity and sensitivity to detect NAFLD. Histological findings showed stage I steatosis in 51.93%, stage II in 28.84% and stage III in 19.23%. Cirrhosis was found in 3.15%. DISCUSSION: Results of our study confirm the high frequency of NAFLD in association with gallstone disease. We consider this the first work to analyze and describe the primary clinical, biochemical and morphological characteristics.

Routine liver biopsy to screen for nonalcoholic fatty liver disease (NAFLD) during cholecystectomy for gallstone disease: is it justified?

BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) and gallstone disease (GD) share common risk factors. There are no firm recommendations regarding screening of NAFLD in patients at risk. Our aim was to assess the prevalence of and factors associated with NAFLD in a cohort of patients operated for symptomatic GD and evaluate the usefulness of routine liver biopsy. METHODS: Ninety-five consecutive patients underwent a liver biopsy at the end of a standard laparoscopic cholecystectomy for symptomatic GD. Clinical, biochemical, demographic, and anthropometric variables were obtained prospectively. RESULTS: Fifty-two patients (55%) had biopsies compatible with NAFLD. These patients were classified according to the system proposed by Brunt et al. as follows: grade I, n = 27 (52%); grade II, n = 15 (29%); grade III, n = 10 (19%). Two grade III patients had zone III focal perisinusoidal fibrosis and three had overt cirrhosis. Only 13% of subjects had a suspected diagnosis of NAFLD preoperatively. In multivariate logistic regression, only obesity was significantly associated with NAFLD. There were no complications or mortality. DISCUSSION: Fifty-five percent of patients with GD have associated NAFLD. Awareness of this association may result in an earlier diagnosis. The high prevalence of NAFLD in patients with GD may justify routine liver biopsy during cholecystectomy to establish the diagnosis, stage, and possible direct therapy.

Frecuencia y características clínicas, bioquímicas e histológicas del hígado graso no alcohólico en pacientes con enfermedad litiásica vesicular / Frequency and clinical, biochemical and histological characteristics of nonalcoholic fatty liver disease in patients with gallstone disease

BACKGROUND: In 1980, nonalcoholic fatty liver disease (NALFD) was described. It is related to the genesis of gallstones and is considered as a manifestation of the metabolic syndrome. In order to determine the frequency, anatomoclinical characteristics and biochemical and histological alterations in NAFLD, patients underwent cholecystectomy (GD). For this reason, we considered carrying out this study. METHODS: This was a prospective and observational study. The study population was comprised of patients with gallstone disease who were treated at the [quot ]Hospital Español[quot ] in Veracruz, Mexico from January 1, 2005 to November 30, 2006 and underwent cholecystectomy and liver biopsy. Analyzed variables were anthropometric characteristics and risk factors, and in each patient biochemical tests, abdominal ultrasound (US) and histological liver study were performed. RESULTS: In 95 patients, according to liver biopsy diagnoses, we found a frequency of 54.74% of NAFLD associated with gallstones. Females were more affected (71.15%) and the average age was 55.6 +/- 17.87 years. Risk factors were obesity (67.3%), diabetes mellitus (17.3%), and dyslipidemia (76.92%). Patients with NAFLD had elevated levels of glucose, glycosylated hemoglobin, cholesterol, triglycerides and HDLcholesterol, and aminotransferases. Abdominal US did not show sufficient specificity and sensitivity to detect NAFLD. Histological findings showed stage I steatosis in 51.93%, stage II in 28.84% and stage III in 19.23%. Cirrhosis was found in 3.15%. DISCUSSION: Results of our study confirm the high frequency of NAFLD in association with gallstone disease. We consider this the first work to analyze and describe the primary clinical, biochemical and morphological characteristics.