Biomedical subjects

N O Strömberg

Publications and source records attributed to N O Strömberg.

8 recordsLinked to original sources

PubMed2001

Error analysis of a natural breathing calibration method for respiratory inductive plethysmography.

Respiratory volumes are measured non-invasively by recording rib cage and abdominal motions using respiratory inductive plethysmography (RIP). Qualitative diagnostic calibration (QDC) of RIP is based on the natural variability in the relative rib-cage-to-abdomen contribution during tidal breathing. ODC does not require subject cooperation but it has previously been shown that accuracy may deteriorate when breathing pattern changes. The aim of this study was to investigate the causes and situations where QDC accuracy deteriorates. The QDC method was compared to PRA (calibration during voluntarily preferential rib cage or abdomen breathing) in ten adults. A reference RIP calibration was obtained from all validation data (REF). The PRA method had better accuracy than the ODC method (p<0.01). The volumetric error ranged between 10% and 136% with QDC and between 5% and 33% with PRA. The PRA calibration factors were within 6% of those from REF, while the QDC rib-cage factor was underestimated by 15% and the abdominal factor was overestimated by 38%. Small natural variability in the relative rib-cage-to-abdomen contribution was related to poor accuracy. Each compartment's variability depended on its magnitude, which is a violation of the QDC assumptions.

Calibration↗

PubMed2000

Ventilation inhomogeneity assessed by nitrogen washout and ventilation-perfusion mismatch by capnography in stable and induced airway obstruction.

Few studies have been published on gas distribution in the lung during acute and stable airway obstruction in children. Multiple breath nitrogen (N(2)) washout is an established method for assessing ventilation inhomogeneity, while the tidal breathing capnogram may be used as an indicator of ventilation-perfusion (V(')(A)/Q) mismatch. We hypothesized that significant V(')(A)/Q mismatch is not seen in stable airway obstruction unless obstruction is severe, and that stable and induced airway obstruction of similar severity would result in different degrees of V(')(A)/Q mismatch. To test this hypothesis, we performed spirometry measurements of forced expiratory volume in 1 sec (FEV(1)), multiple breath N(2) washout, and tidal breathing capnography in 11 young patients (9-30 years) with cystic fibrosis, 37 asthmatic patients (8-18 years), and 34 healthy subjects (7-20 years). Lung function was measured at rest, after airway obstruction induced by cold dry air hyperventilation or methacholine challenge, and after beta(2)-agonist treatment. V(')(A)/Q mismatch was assessed from the slopes of the phases II and III of the capnogram. We observed a normal capnogram during stable obstruction of moderate severity despite significant ventilation inhomogeneity. In patients with severe stable obstruction and in those with induced airway obstruction significant ventilation inhomogeneity and pathological capnograms were seen. Induced airway obstruction, resulted in a more pathological capnogram than stable obstruction of similar severity. beta(2)-agonist treatment reduced ventilation inhomogeneity, but did not improve the capnogram. Our findings are compatible with the presence of an efficient pulmonary blood flow regulatory mechanism that adequately compensates for chronic ventilation inhomogeneity of moderate severity, but not for severe or sudden airway obstruction.

Adolescent↗

PubMed1999

Improved accuracy and extended flow range for a Fleisch pneumotachograph.

A large linear flow range and a small instrumental dead space volume are incompatible properties for a pneumotachometer (PTM). The linearity of a Fleisch number 2 PTM is studied for flows up to 6 litre s-1 (nominal range 0-2 litre s-1) with various up- and downstream geometries. It is hypothesised that using an array of calibration factors (conductance; flow/pressure), instead of a single calibration factor over the entire flow range, could improve accuracy and also extend the applicable flow range. The conductance against pressure characteristics are calculated with a previously described weighted averaging technique based on multiple strokes from a precision syringe. A single conductance value gives stroke volume errors in the range of -5 to 3% (0-2 litre s-1) and -6 to 11% (0-6 litre s-1) for validation using the same geometry as for calibration. The pressure dependent conductance improves accuracy to within -3% and 1% independent of flow range. However, for validation using a different geometry than for calibration, errors range from -5% to +8%. The degree of non-linearity varies between the geometries (range 3-15%) and is highest when using a one-directional valve upstream of the PTM and a Y-shaped connector. In conclusion, a pressure-dependent conductance improves accuracy and can also be used to extend the applicable flow range up to at least three times the nominal flow range.

Calibration↗

PubMed1998

Thoracoabdominal asynchrony in small children with lung disease--methodological aspects and the relationship to lung mechanics.

Thoracoabdominal asynchrony (TAA) has been regarded as a clinical sign of lung disease. A measure of TAA is the phase angle (phi) between ribcage (RC) and abdominal (ABD) respiratory motion. The aim of this study was to assess the effect of the points chosen for phi calculation. The influence of correct respiratory timing was assessed by calculating TAA indices using a pneumotachometer (PTM) as timing reference and using the calibrated respiratory inductive plethysmograph (RIP) signal for respiratory timing. The relationship between TAA and lung mechanics was studied in 15 young children 9 months to 2.5 years of age with a wide span of restrictive and/or obstructive lung disease. phi as calculated from mid-RC points was poorly related to phi as calculated from the top RC and ABD positions, indicating non-sinusoidal respiratory motions. The estimation of the TAA indices depended on correct respiratory timing, which in the case of severe asynchrony cannot be inferred from the RIP signals alone. An external source for respiratory timing, such as the airway flow measured by a PTM, is needed. The degree of asynchronous chest wall movement was only a weak indicator of pathological lung mechanics. We conclude that the usefulness of TAA indices as indicators of impaired lung mechanics is limited by the sensitivity to the points used for their calculation (phi) and the need of an external source for respiratory timing. It was therefore not surprising that a rather weak relationship was seen between TAA indices and lung mechanics.

Abdomen↗

PubMed1996

Breathing pattern variability during bronchial histamine and methacholine challenges in asthmatics.

Breathing pattern variability was determined in 10 asthmatic adolescents during repeated bronchial histamine and methacholine challenges (HiCh/MeCh). The purpose was to provide information on ventilatory control in asthmatics by comparing the variability of the various breathing pattern parameters at rest and during induced bronchial obstruction. Changes in variability during bronchial obstruction might be explained by either anxiety effects causing increased variability or by the minimization of the work of breathing causing decreased variability. Ventilation was monitored by respiratory inductive plethysmography in order to minimize the effects on the spontaneous pattern of breathing. Breath-to-breath and day-to-day variability were determined concerning respiratory frequency (fR), inspiratory tidal volume (VTI), inspiratory ventilation (V'I), inspiratory time to total cycle time ratio (TI/TTOT), mean inspiratory flow (VTI/TI, an index of ventilatory drive), rib cage fraction of VTI (VRC/VTI), and maximum compartmental amplitude to VTI ratio (MCA/VTI; an index of rib cage and abdominal phasing). No difference in any parameter was found regarding breath-to-breath coefficient of variation (CV = SD/mean) between recordings at baseline, after saline inhalation and after threshold dose of the provocative agents, i.e. > 20% fall in FEV1. Variability was less for MCA/VTI and VRC/VTI (mean CV 1.3 and 7.7%, respectively) than for TI/TTOT, fR, VTI/TI, VTI, and V'I (14.2, 15.8, 20.9, 22.2 and 21.1%, respectively) (P < 0.01). Likewise, the day-to-day variability did not differ in any parameter between recordings at baseline, after saline inhalation and after threshold dose. The variability was less for MCA/VTI (0.7%) than for TI/TTOT, VRC/VTI, V'I, VTI/TI, fR and VTI (7.1, 12.1, 12.8, 14.2, 13.0 and 15.4%) (P < 0.05). Furthermore, TI/TTOT was less variable than VTI (P < 0.05). Thus, the ventilatory pattern was quite reproducible on a day-to-day basis, despite considerable breath-to-breath variability. Ventilatory drive and tidal volumes were more variable than the rib cage and abdominal phasing, the respiratory timing and the rib cage fraction of tidal volume. The lack of difference in variability between rest and induced bronchial obstruction indicates that other factors than anxiety or minimization of the work of breathing are important for the control of respiration in asthmatics during bronchial challenge.

Administration, Inhalation↗

PubMed1996

Hyperventilation during bronchial challenges in asthmatics: reproducibility and assessment of contributing factors.

Among asthmatics, the ventilatory response is heterogeneous during bronchial challenge. This study aimed to investigate the reproducibility of the response and to assess possible causes for hyperventilation. Repeated bronchial histamine and methacholine challenges (HiCh/MeCh) were performed in 10 asthmatic adolescents. Ventilation was monitored by respiratory inductive plethysmography (RIP), in order to minimally affect the spontaneous breathing pattern. FEV1 and the volume of trapped gas (measured as the volume of air mobilized by five maximal breaths after a multiple breath nitrogen washout to 2% N2), were used to assess mainly central and peripheral airways obstruction, respectively. When FEV1 had decreased by at least 20%, mean inspiratory flow (VTI/TI) increased by 21% and minute ventilation (V'I) by 21% and 23% during HiCh and MeCh, respectively (both P < 0.05). No correlation was found between the magnitude of the ventilatory response and either: the degree of FEV1 decline, the increase in gas trapping, SaO2 decline or the increase in dyspnoea score. Histamine challenge after beta 2-agonist pre-treatment was associated with increased ventilatory drive in one patient despite the absence of bronchial obstruction, indicating that histamine might directly stimulate afferent airway nerves which cause hyperventilation. The intra-individual variability of the ventilatory response (increase in V'I and VTI/TI) was more than 100% of the mean ventilatory response, while the variability of the bronchomotor response was about 25% of the mean bronchomotor response. Thus, during induced bronchial obstruction in asthmatics, the occurrence of hyperventilation and its intensity are not related to either the degree of central or peripheral airways obstruction, or to the degree of dyspnoea. The reproducibility of the ventilatory response is poor. The ventilatory response appears to be the result of a complex interaction between several afferent stimuli and central ventilatory control.

Administration, Inhalation↗

PubMed1993

Evaluation of various models for respiratory inductance plethysmography calibration.

We evaluated one nonlinear and two linear models of the ventilatory system while calibrating the respiratory inductance plethysmograph (RIP) against a pneumotachometer. A calibration method involving voluntary varying rib cage and abdominal contributions to tidal volume in a single body position was utilized. The influence on accuracy of the choice of respiratory phase during calibration was assessed. Both tidal and intratidal volumes were evaluated. Ten adults with no history of respiratory disorders went through RIP calibration and validation in the sitting and supine positions. A linear calibration model, relating lung volume changes from the start of inspiration or expiration to rib cage and abdominal excursions from initiation of respiratory motion, had the best accuracy. The choice of respiratory phase for calibration did not affect accuracy. RIP generally underestimated lung volume at the start of inspiration and overestimated lung volume at the end of inspiration. RIP was more accurate in the supine than the sitting position, probably because of limited spine flexion in the supine position.

Adult↗

PubMed1993

Ventilatory pattern during bronchial histamine challenge in asthmatics.

We wanted to investigate whether asthmatic subjects change their ventilatory pattern consistently when forced expiratory volume in one second (FEV1) has declined by at least 20% during bronchial histamine challenge, in order to assess whether respiratory pattern analysis can be used to monitor bronchial obstruction continuously. Histamine challenge was performed twice within a four week period, in eight asthmatic teenagers. Respiratory inductive plethysmography (RIP) was used for respiratory pattern evaluation, whilst the patients breathed on a mouthpiece attached to a pneumo-tachometer (PTM) whilst wearing a noseclip (first histamine challenge), and during natural breathing (second HiCh). End-tidal carbon dioxide tension (PETCO2) was measured on both occasions. During the second histamine challenge, four of the eight patients responded with a 72% (mean) increase in minute ventilation (VE), an 80% increase in mean inspiratory flow (VI), and a 20% decrease in PETCO2. VE and VI were unchanged, or tended to decrease, among the other four patients (ventilatory nonresponders). Neither provocative dose producing a 20% fall in FEV1 (PD20) to histamine nor the magnitude of the fall in FEV1 differed between ventilatory responders and nonresponders. The ventilatory response to inhaled histamine was abolished when breathing through a PTM. Histamine induced bronchospasm is not uniformly reflected in the breathing pattern. Hyperventilation during histamine challenge might be the consequence of vagal airway receptor activation. Respiratory pattern analysis is not a feasible way to monitor bronchial obstruction during histamine challenge.

Adolescent↗