Presión intraabdominal y torácica en pacientes críticos con sospecha de hipertensión intraabdominal / Intraabdominal and thoracic pressure in critically ill patients with suspected

ObjetivoAnalizar la correlación entre la presión intraabdominal e intratorácica en pacientes con sospecha de hipertensión intraabdominal (HIA).DiseñoEstudio prospectivo observacional de una cohorte.ÁmbitoUnidad de medicina intensiva polivalente de un hospital universitario.PacientesSe incluyó a 27 pacientes medicoquirúrgicos dependientes de ventilación mecánica controlada por fallo respiratorio agudo y con factores de riesgo de hipertensión intraabdominal.Principales variablesMedimos las presiones intraabdominal (PIA), esofágica (Peso) y de la vía aérea en condiciones estáticas (est) y dinámicas (din). Calculamos la distensibilidad del sistema respiratorio (Csr), pulmón (Cp) y pared torácica (Cpt).ResultadosEn 10 pacientes la PIAest fue mayor de 12mmHg (HIA, PIAest, 14±2 [12-21] mmHg) y en el resto fue normal (n=17; PIAest, 8±2 [3-11] mmHg). La Pesoest fue 11±5 (2-27) y Pesodin, 7±4 (2-24) cmH2O. Considerando la presencia o no de HIA, Pesoest fue 9±4 vs. 7±3cmH2O (p=0,2) y Pesodin, 6±2 vs. 4±3cmH2O (p=0,3), respectivamente. La correlación de Pesoest y din con PIAest fue 0,5 (p=0,003) y 0,4 (p=0,03), respectivamente. Los componentes de la distensibilidad del sistema respiratorio estaban disminuidos (Csr, 31±8; Cp, 52±22; Cpt, 105±50ml/cmH2O), Cpt fue significativamente más baja en los pacientes con HIA (81±31 vs. 118±55ml/cmH2O; p=0,02). El coeficiente de correlación entre la PIAest y Cpt fue –0,7 (p<0,001) y de –0,5 (p=0,002) con Csr.ConclusionesLa pared torácica es más rígida en pacientes con hipertensión abdominal. En presencia de factores de riesgo de HIA las presiones en estos compartimentos son muy variables (AU)

Objective: To study the correlation between intraabdominal and intrathoracic pressure inpatients with suspected intraabdominal hypertension.Design: A prospective, observational cohort study.Setting: Polyvalent intensive care unit of a University hospital.Patients: Twenty-seven medical-surgical patient dependent upon controlled mechanical ventilationdue to acute respiratory failure and with several risk factors for intraabdominalhypertension (IAH).Main variables: Intraabdominal (IAP), esophageal (Peso) and airways pressure were measuredunder static (st) and dynamic (dyn) conditions. Respiratory system (Crs), lung (Cl) and chestwall compliance (Ccw)were calculated.Results: In 10 patients IAP > 12mmHg (IAH, IAPst, 14±2 [12-21] mmHg), while in the rest thepressure proved normal (n = 17; IAPst, 8±2 [3-11] mmHg). Peso st was 11±5 (2-27) and Pesodyn 7±4 (2-24) cmH2O. Depending on the presence or absence of IAH, Peso st was 9±4 vs7±3 cmH2O (p = 0.2) and Peso dyn 6±2 vs 4±3 cmH2O (p = 0.3), respectively. The correlationbetween Peso st and dyn with IAPst was 0.5 (p = 0.003) and 0.4 (p = 0.03), respectively. Thecompliance components were decreased (Crs, 31±8; Cl, 52±22 and Ccw, 105±50 ml/cmH2O);Ccw was significantly lower in patients with IAH (81±31 vs 118±55 ml/cmH2O; p = 0.02). Thecorrelation coefficient between IAPst and Ccw was —0.7 (p < 0.001), and —0.5 (p = 0.002) withrespect to Crs.Conclusions: A stiffer chest wall was observed in patients with IAH. In patients with risk factorsfor IAH, pressures in these compartments were highly variable (AU)

[Intraabdominal and thoracic pressure in critically ill patients with suspected intraabdominal hypertension]. / Presión intraabdominal y torácica en pacientes críticos con sospecha de hipertensión intraabdominal.

OBJECTIVE: To study the correlation between intraabdominal and intrathoracic pressure in patients with suspected intraabdominal hypertension. DESIGN: A prospective, observational cohort study. SETTING: Polyvalent intensive care unit of a University hospital. PATIENTS: Twenty-seven medical-surgical patient dependent upon controlled mechanical ventilation due to acute respiratory failure and with several risk factors for intraabdominal hypertension (IAH). MAIN VARIABLES: Intraabdominal (IAP), esophageal (Peso) and airways pressure were measured under static (st) and dynamic (dyn) conditions. Respiratory system (Crs), lung (Cl) and chest wall compliance (Ccw)were calculated. RESULTS: In 10 patients IAP > 12 mmHg (IAH, IAPst, 14 ± 2 [12-21] mmHg), while in the rest the pressure proved normal (n = 17; IAPst, 8 ± 2 [3-11] mmHg). Peso st was 11 ± 5 (2-27) and Peso dyn 7 ± 4 (2-24) cmH2O. Depending on the presence or absence of IAH, Peso st was 9 ± 4 vs 7 ± 3 cmH2O (p = 0.2) and Peso dyn 6 ± 2 vs 4 ± 3 cmH2O (p = 0.3), respectively. The correlation between Peso st and dyn with IAPst was 0.5 (p= 0.003) and 0.4 (p = 0.03), respectively. The compliance components were decreased (Crs, 31 ± 8; Cl, 52 ± 22 and Ccw, 105 ± 50 ml/cmH2O); Ccw was significantly lower in patients with IAH (81 ± 31 vs 118 ± 55 ml/cmH2O; p = 0.02). The correlation coefficient between IAPst and Ccw was -0.7 (p < 0.001), and -0.5 (p = 0.002) with respect to Crs. CONCLUSIONS: A stiffer chest wall was observed in patients with IAH. In patients with risk factors for IAH, pressures in these compartments were highly variable.

[Atrioventricular block in unstable angina. Results of the ARIAM registry]. / Bloqueo auriculoventricular en la angina inestable. Resultados del registro ARIAM.

OBJECTIVE: Describe the frequency of high degree atrioventricular block (HDAVB) in patients with unstable angina (UA), analyze the variables associated with their appearance and evaluate whether HDAVB is independently associated with increased mortality or increased length of ICU stay. DESIGN: Retrospective descriptive study of patients with UA included in the ARIAM registry. SETTING: ICUs from 129 hospitals in Spain. PATIENTS: From June 1996 to December 2003 a total of 14,096 patients were included in the ARIAM registry with a diagnosis of UA. MAIN VARIABLES OF INTEREST: Variables associated with the development of HDAVB, variables associated with the mortality of patients with UA, variables associated with the length of ICU stay of patients with UA. RESULTS: HDAVB frequency was 1%. Development of HDAVB was independently associated with the Killip classification and the presence of sustained ventricular tachycardia or ventricular fibrillation. Crude mortality of patients was significantly increased when HDAVB was present (9% versus 1%, p < 0,001). When adjusted for other variables, HDAVB was not associated with increased mortality. Development of HDAVB in patients with UA was independently associated with an increase in the length of ICU stay (adjusted odds ratio 1.89: 95% confidence interval: 1.33-5.69). CONCLUSIONS: Patients with UA complicated with HDAVB represent a high-risk population with an increased ICU stay.

Bloqueo auriculoventricular en la angina inestable. Resultados del registro ARIAM / Atrioventricular block in unstable angina. Results of the ARIAM registry

Objetivo. Describir la frecuencia de bloqueo auriculoventricular (BAVAG) en los pacientes con angina inestable (AI), analizar las variables asociadas al desarrollo del mismo y evaluar si el BAVAG se asocia de manera independiente con aumento de la mortalidad o de la estancia en Unidades de Cuidados Intensivos (UCI). Diseño. Estudio descriptivo retrospectivo de los pacientes con AI incluidos en el estudio ARIAM. Ámbito. UCI de 129 hospitales españoles. Pacientes. Desde junio de 1996 a diciembre de 2003 se incluyeron en el proyecto ARIAM 14.096 pacientes con diagnóstico de AI. Variables de interés principales. Variables asociadas con el desarrollo de BAVAG, con la mortalidad de los pacientes con AI y con la duración de la estancia en UCI de los pacientes con AI. Resultados. La frecuencia de BAVAG durante el ingreso en UCI fue del 1%. El desarrollo de BAVAG se asoció de manera independiente con el grado en la clasificación de Killip y la presencia de taquicardia ventricular sostenida o de fibrilación ventricular. La mortalidad cruda de los pacientes con AI aumentó significativamente en presencia de BAVAG (9% frente a 1%, p < 0,001). Cuando se ajustó para otras variables no se observó un aumento de la mortalidad asociada al BAVAG. El desarrollo de BAVAG en los pacientes con AI se asocia de manera independiente con un aumento de la estancia media (odds ratio ajustada 1,89; intervalo de confianza del 95%: 1,33-5,69). Conclusiones. Los pacientes con AI que desarrollan BAVAG representan una población de alto riesgo. El BAVAG se asocia con un incremento de la estancia media

Objective. Describe the frequency of high degree atrioventricular block (HDAVB) in patients with unstable angina (UA), analyze the variables associated with their appearance and evaluate whether HDAVB is independently associated with increased mortality or increased length of ICU stay. Design. Retrospective descriptive study of patients with UA included in the ARIAM registry. Setting. ICUs from 129 hospitals in Spain. Patients. From June 1996 to December 2003 a total of 14,096 patients were included in the ARIAM registry with a diagnosis of UA. Main variables of interest. Variables associated with the development of HDAVB, variables associated with the mortality of patients with UA, variables associated with the length of ICU stay of patients with UA. Results. HDAVB frequency was 1%. Development of HDAVB was independently associated with the Killip classification and the presence of sustained ventricular tachycardia or ventricular fibrillation. Crude mortality of patients was significantly increased when HDAVB was present (9% versus 1%, p < 0,001). When adjusted for other variables, HDAVB was not associated with increased mortality. Development of HDAVB in patients with UA was independently associated with an increase in the length of ICU stay (adjusted odds ratio 1.89: 95% confidence interval: 1.33-5.69). Conclusions. Patients with UA complicated with HDAVB represent a high-risk population with an increased ICU stay

[The CRUSADE study, evaluation model of quality in percutaneous coronary intervention]. / El estudio Crusade, modelo de evaluación de la calidad en la intervención coronaria percutánea.

Improvement of care quality does not end with the publication of clinical trials that show clinical evidence of effectiveness or with its support by the different international therapeutic guides. This quality improvement requires evaluation in the real population. This can be done by analysis of clinical registries, that would evaluate adequate compliance of the clinical guides and their effectiveness in the real population. The CRUSADE study is a study that evaluates use, prognosis and factors of prediction, of invasive strategy by early percutaneous coronary intervention (PCI) (first 48 hours of the ischemic event) in high-risk patients with non-ST segment elevation acute coronary syndrome (NSTE-ACS). Of the 17,926 patients studied, 8037 (44.8%) underwent cardiac catheterism in the first 48 hours of the ischemic event. Intrahospital mortality of the invasive strategy was significantly less than medical treatment (2.5% versus 3.7%). The patients who underwent an early invasive strategy were a selected population, as the more solid independent prediction factors were associated to early invasive treatment: cardiology care, earlier age, absence of renal failure, absence of heart failure both previously or on arrival to the hospital and lower heart rate. Finally, it could be concluded that, in spite of the decrease of mortality achieved with the early invasive strategy, this would not done in most of the patients, being reserved for subgroups with lower comorbidity and for those seen by the cardiologists.

El estudio Crusade, modelo de evaluación de la calidad en la intervención coronaria percutánea / The Crusade study, evaluation model of quality in percutaneous coronary intervention

La mejora de la calidad asistencial no finaliza con la publicación de ensayos clínicos que demuestran evidencia clínica de efectividad, ni por su respaldo por las distintas guías terapéuticas internacionales. Esta mejora de la calidad requiere una evaluación en la población real, ello se puede realizar mediante el análisis de registros clínicos, que valorarían el adecuado cumplimiento de las guías clínicas y su efectividad en la población real. El estudio CRUSADE es un estudio que evalúa la utilización, el pronóstico y los factores de predicción de la estrategia invasiva mediante la intervención coronaria percutánea (ICP) precoz (primeras 48 horas del evento isquémico), en pacientes con síndrome coronario agudo sin elevación del segmento ST (SCASEST) de alto riesgo. De los 17.926 pacientes estudiados, a 8.037 (44,8%) se les realiza cateterismo cardíaco en las primeras 48 horas del evento isquémico. La mortalidad intrahospitalaria de la estrategia invasiva fue significativamente menor que el tratamiento médico (2,5% frente a 3,7%). Los pacientes a los que se les realizó una estrategia invasiva precoz representaban una población seleccionada, al ser los factores independientes de predicción más sólidos, asociados al tratamiento invasivo precoz: la asistencia cardiológica, la edad más joven, la ausencia de insuficiencia renal, ausencia de insuficiencia cardíaca previa, o a la llegada al hospital y una frecuencia cardíaca más baja. Pudiéndose concluir finalmente, que a pesar de la disminución de la mortalidad conseguida con la estrategia invasiva precoz, ésta no se realiza en la mayoría de los pacientes, quedando reservada para subgrupos de menor comorbilidad, y para aquellos atendidos por los cardiólogos

Improvement of care quality does not end with the publication of clinical trials that show clinical evidence of effectiveness or with its support by the different international therapeutic guides. This quality improvement requires evaluation in the real population. This can be done by analysis of clinical registries, that would evaluate adequate compliance of the clinical guides and their effectiveness in the real population. The CRUSADE study is a study that evaluates use, prognosis and factors of prediction, of invasive strategy by early percutaneous coronary intervention (PCI) (first 48 hours of the ischemic event) in high-risk patients with non-ST segment elevation acute coronary syndrome (NSTE-ACS). Of the 17926 patients studied, 8037 (44.8%) underwent cardiac catheterism in the first 48 hours of the ischemic event. Intrahospital mortality of the invasive strategy was significantly less than medical treatment (2.5% versus 3.7%). The patients who underwent an early invasive strategy were a selected population, as the more solid independent prediction factors were associated to early invasive treatment: cardiology care, earlier age, absence of renal failure, absence of heart failure both previously or on arrival to the hospital and lower heart rate. Finally, it could be concluded that, in spite of the decrease of mortality achieved with the early invasive strategy, this would not done in most of the patients, being reserved for subgroups with lower comorbidity and for those seen by the cardiologists

[Thrombolysis in cardiac arrest]. / Trombolisis en la parada cardíaca.

Both acute myocardial infarction and pulmonary thromboembolism are responsible for a great number of cardiac arrests. Both present high rates of mortality. Thrombolysis has proved to be an effective treatment for acute myocardial infarction and pulmonary thromboembolism with shock. It would be worth considering whether thrombolysis could be effective and safe during or after cardiopulmonary resuscitation (CPR). Unfortunately, too few clinical studies presenting sufficient scientific data exist in order to respond adequately to this question. However, most studies they show that thrombolysis applied during and after CPR is a therapeutic option that is not associated with greater risk of serious hemorrhaging and could possibly have beneficial effects. On the other hand, experimental data exists which show that thrombolytics can attenuate neurological damage produced after CPR. Nevertheless, clinical trials would be necessary in order to adequately establish the effectiveness and safety of thrombolysis in patients who require CPR.

[Neurogenic stunned myocardium]. / Aturdimiento miocáirdico neurogénico.

The existence of stunned myocardium and reversible myocardial dysfunction is widely described and accepted in patients suffering ischemic heart disease. However, it cannot be exclusive to coronary disease. Classically, the appearance of electrocardiographic changes in the critical neurological disease has been described. However, at present, it seems to be observed that some of these patients with critical neurological disease could have variable grades of myocardial dysfunction, which is generally reversible in the surviving patients. This myocardial dysfunction, which could affect critically ill neurological patients, has traits similar to stunned myocardium generated in coronary patients since: a) it is generally associated to electrocardiographic changes, b) it can be accompanied by segmental contractility disorders and even c) it may be accompanied by a certain increase of cardiac biomarkers. Although its etiopathogeny is unknown, it could be related with the severity of the primary neurological disease. Its prophylaxis and prognosis are also unknown. It could be related with neurogenic edema, with hemodynamic instability, and could also play a very important role in brain death and in organ donation.

Trombolisis en la parada cardíaca / Thrombolysis in cardiac arrest

Tanto el infarto agudo de miocardio como el tromboembolismo pulmonar son responsables de un gran número de paradas cardiorrespiratorias, presentando éstos una altísima mortalidad. La trombolisis se ha mostrado eficiente como tratamiento del infarto agudo de miocardio y del tromboembolismo pulmonar que cursa con shock. Se podría plantear si la trombolisis es eficaz y segura durante o tras las maniobras de reanimación cardiopulmonar. Desgraciadamente, existen muy pocos estudios clínicos con un nivel suficiente de evidencia científica para responder satisfactoriamente a esta pregunta. No obstante, la mayoría de los estudios muestran que la trombolisis aplicada durante y tras la reanimación cardiopulmonar es una opción terapéutica que no se asocia con un mayor riesgo de complicaciones hemorrágicas graves y que podría tener un posible efecto beneficioso. Por otra parte, existen datos experimentales que muestran que los trombolíticos pueden atenuar el daño neurológico producido tras la reanimación cardiopulmonar. Sin embargo, para establecer de manera adecuada cuál es la eficacia y la seguridad de la trombolisis en los pacientes que requieren reanimación cardiopulmonar sería necesario realizar un ensayo clínico

Both acute myocardial infarction and pulmonary thromboembolism are responsible for a great number of cardiac arrests. Both present high rates of mortality. Thrombolysis has proved to be an effective treatment for acute myocardial infarction and pulmonary thromboembolism with shock. It would be worth considering whether thrombolysis could be effective and safe during or after cardiopulmonary resuscitation (CPR). Unfortunately, too few clinical studies presenting sufficient scientific data exist in order to respond adequately to this question. However, most studies they show that thrombolysis applied during and after CPR is a therapeutic option that is not associated with greater risk of serious hemorrhaging and could possibly have beneficial effects. On the other hand, experimental data exists which show that thrombolytics can attenuate neurological damage produced after CPR. Nevertheless, clinical trials would be necessary in order to adequately establish the effectiveness and safety of thrombolysis in patients who require CPR

Aturdimiento miocárdico neurogénico / Neurogenic stunned myocardium

La existencia del aturdimiento miocárdico y de disfunción miocárdica reversible está ampliamente descrita y aceptada en los pacientes afectos de cardiopatía isquémica, no obstante puede no ser exclusiva de la patología coronaria. Clásicamente ha sido descrita la aparición de cambios electrocardiográficos en la patología crítica neurológica, sin embargo en la actualidad parece observarse que algunos de estos pacientes, con patología crítica neurológica, podrían presentar grados variables de disfunción miocárdica, que suele ser reversible en los pacientes supervivientes. Esta disfunción miocárdica, que podría afectar a los pacientes neurológicos críticamente enfermos, presenta rasgos similares al aturdimiento miocárdico generado sobre pacientes coronarios, pues: a) suele asociarse a cambios electrocardiográficos, b) podría acompañarse de trastornos de contractilidad segmentaria, e incluso c) puede acompañarse de cierta elevación de biomarcadores cardíacos. Si bien su etiopatogenia es desconocida, podría relacionarse con la gravedad de la patología neurológica primaria. También se ignora su profilaxis y su pronóstico, pudiendo estar relacionada con el edema neurogénico, con la inestabilidad hemodinámica, y además desempeñar un rol muy importante en la muerte cerebral y ante la donación de órganos

The existence of stunned myocardium and reversible myocardial dysfunction is widely described and accepted in patients suffering ischemic heart disease. However, it cannot be exclusive to coronary disease. Classically, the appearance of electrocardiographic changes in the critical neurological disease has been described. However, at present, it seems to be observed that some of these patients with critical neurological disease could have variable grades of myocardial dysfunction, which is generally reversible in the surviving patients. This myocardial dysfunction, which could affect critically ill neurological patients, has traits similar to stunned myocardium generated in coronary patients since: a) it is generally associated to electrocardiographic changes, b) it can be accompanied by segmental contractility disorders and even c) it may be accompanied by a certain increase of cardiac biomarkers. Although its etiopathogeny is unknown, it could be related with the severity of the primary neurological disease. Its prophylaxis and prognosis are also unknown. It could be related with neurogenic edema, with hemodynamic instability, and could also play a very important role in brain death and in organ donation

Proyecto ARIAM: décimo aniversario / ARIAM Project: tenth anniversary

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Cambios en la auto-PEEP durante la ventilación mecánica relacionados con la frecuencia respiratoria según el análisis de la constante de tiempo / Changes in auto-peep during mechanical ventilation associated with respiratory steady according to time-constant analysis

Objetivo. El análisis de la constante de tiempo espiratorio (tau) indica el tiempo necesario para que el sistema respiratorio alcance un estado estable. Estudiamos, durante la ventilación mecánica controlada, si el ajuste de la frecuencia respiratoria, según el valor de tau, puede reducir o eliminar la auto-PEEP (presión positiva telespiratoria). Diseño. Estudio clínico prospectivo de una cohorte de pacientes en ventilación mecánica. Ámbito. Unidad de medicina intensiva de un hospital universitario. Pacientes y método. Estudiamos a 17 pacientes con lesión pulmonar aguda (n = 10) o con insuficiencia respiratoria crónica agudizada (n = 7). En ventilación mecánica controlada, medimos la mecánica respiratoria, la auto-PEEP estática y el valor de tau en la fase espiratoria de la curva de volumen (V[t] = V0 e -[t/RC] + b). Conociendo el valor de tau, cambiamos la frecuencia respiratoria manteniendo el volumen por minuto constante (TE = tau × 4, I:E = 0,5) y analizamos el cambio en la auto-PEEP y mecánica respiratoria. Resultados. El valor de la constante b fue 0,02 (0,04) l y se correlacionó con el valor de tau (r = 0,8). En los pacientes con insuficiencia respiratoria crónica agudizada, el valor de tau fue de 1,04 (0,44) s, y la frecuencia respiratoria fue disminuida de 13,49 (2,87) a 11,72 (3,07) respiraciones/min (p = 0,06), sin un descenso significativo en la auto-PEEP (5,29 [5,11] a 4,87 [5,21] cmH2O). En los pacientes con lesión pulmonar aguda, tau fue de 0,53 (0,16) s y la frecuencia respiratoria fue aumentada desde 15,22 (2,74) a 20,62 (7,26) respiraciones/min (p = 0,05), sin modificar significativamente la auto-PEEP (2,80 [2,03] a 2,40 [1,67] cmH2O). Conclusiones. El análisis de la constante de tiempo no permitió disminuir la auto-PEEP en los pacientes con insuficiencia respiratoria crónica agudizada (FRCA). En el grupo con lesión pulmonar aguda fue posible utilizar frecuencias respiratorias elevadas sin aumentar la auto-PEEP (AU)

Results of respiratory mechanics analysis in the critically ill depend on the method employed.

OBJECTIVE: To compare the measurements of total resistance and dynamic elastance determined by different techniques of respiratory mechanics analysis based on the time or frequency domains. DESIGN: Prospective study. SETTING: A 12-bed medical and surgical intensive care unit in a 700-bed university hospital. PATIENTS: Eighteen sedoparalyzed patients who needed controlled mechanical ventilation for acute or chronic acute respiratory failure. MEASUREMENTS: The total resistance and dynamic elastance in the time domain were determined by the occlusion technique and by multiple linear regression. The Fourier analysis was used to study the impedance of the respiratory system for elastance and resistance values in the frequency domain. RESULTS: The ANOVA analysis of the elastance variable showed no statistical differences (Ef: 41.4+/-19.0 cmH(2)O/l, Emlr: 40.8+/-17.2 cmH(2)O/l Edyn,occ: 39.5+/-14.0 cmH(2)O/l; ns) and the correlation was very good (r=0.8-0.9). The total resistances were less with multiple linear regression (13.5+/-9.3 cmH(2)O/l per s, p<0.05) than Rmax (17.0+/-11.9 cmH(2)O/l per s) or Rf (17.6+/-10.2 cmH(2)O/l per s). There were no differences between Rmax and Rf (p=0.7) and the correlation between resistances was 0.7-0.9. The agreement analysis for variables without statistical differences showed the following limits: Edyn,occ-f: -17 to 13 cmH(2)O/l; Edyn,occ-mlr: -12 to 9 cmH(2)O/l; Emlr-f: -6 to 8 cmH(2)O/l; Rmax-f: -18 to 19 cmH(2)O/l per s. This last range was related to the autoPEEP level (r=0.9). CONCLUSION: The wide agreement limits show that respiratory mechanics analysis is very dependent on the measurement technique used, particularly for resistance, perhaps due to the higher dependence on frequency.