Search for Subsolar-Mass Binaries in the First Half of Advanced LIGO's and Advanced Virgo's Third Observing Run

We report on a search for compact binary coalescences where at least one binary component has a mass between 0.2  M_{⊙} and 1.0  M_{⊙} in Advanced LIGO and Advanced Virgo data collected between 1 April 2019 1500 UTC and 1 October 2019 1500 UTC. We extend our previous analyses in two main ways: we include data from the Virgo detector and we allow for more unequal mass systems, with mass ratio q≥0.1. We do not report any gravitational-wave candidates. The most significant trigger has a false alarm rate of 0.14  yr^{-1}. This implies an upper limit on the merger rate of subsolar binaries in the range [220-24200]  Gpc^{-3} yr^{-1}, depending on the chirp mass of the binary. We use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. One is an isotropic distribution of equal-mass primordial black holes. Using this model, we find that the fraction of dark matter in primordial black holes in the mass range 0.2  M_{⊙}<m_{PBH}<1.0  M_{⊙} is f_{PBH}≡Ω_{PBH}/Ω_{DM}≲6%. This improves existing constraints on primordial black hole abundance by a factor of ∼3. The other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. The upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at M_{min}=1  M_{⊙}, where f_{DBH}≡Ω_{DBH}/Ω_{DM}≲0.003%. These are the first constraints placed on dissipative dark models by subsolar-mass analyses.

Point Absorber Limits to Future Gravitational-Wave Detectors

High-quality optical resonant cavities require low optical loss, typically on the scale of parts per million. However, unintended micron-scale contaminants on the resonator mirrors that absorb the light circulating in the cavity can deform the surface thermoelastically and thus increase losses by scattering light out of the resonant mode. The point absorber effect is a limiting factor in some high-power cavity experiments, for example, the Advanced LIGO gravitational-wave detector. In this Letter, we present a general approach to the point absorber effect from first principles and simulate its contribution to the increased scattering. The achievable circulating power in current and future gravitational-wave detectors is calculated statistically given different point absorber configurations. Our formulation is further confirmed experimentally in comparison with the scattered power in the arm cavity of Advanced LIGO measured by in situ photodiodes. The understanding presented here provides an important tool in the global effort to design future gravitational-wave detectors that support high optical power and thus reduce quantum noise.

Approaching the motional ground state of a 10-kg object

The motion of a mechanical object, even a human-sized object, should be governed by the rules of quantum mechanics. Coaxing them into a quantum state is, however, difficult because the thermal environment masks any quantum signature of the object's motion. The thermal environment also masks the effects of proposed modifications of quantum mechanics at large mass scales. We prepared the center-of-mass motion of a 10-kilogram mechanical oscillator in a state with an average phonon occupation of 10.8. The reduction in temperature, from room temperature to 77 nanokelvin, is commensurate with an 11 orders-of-magnitude suppression of quantum back-action by feedback and a 13 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state. Our approach will enable the possibility of probing gravity on massive quantum systems.

Constraints on Cosmic Strings Using Data from the Third Advanced LIGO-Virgo Observing Run

We search for gravitational-wave signals produced by cosmic strings in the Advanced LIGO and Virgo full O3 dataset. Search results are presented for gravitational waves produced by cosmic string loop features such as cusps, kinks, and, for the first time, kink-kink collisions. A template-based search for short-duration transient signals does not yield a detection. We also use the stochastic gravitational-wave background energy density upper limits derived from the O3 data to constrain the cosmic string tension Gμ as a function of the number of kinks, or the number of cusps, for two cosmic string loop distribution models. Additionally, we develop and test a third model that interpolates between these two models. Our results improve upon the previous LIGO-Virgo constraints on Gμ by 1 to 2 orders of magnitude depending on the model that is tested. In particular, for the one-loop distribution model, we set the most competitive constraints to date: Gμ≲4×10^{-15}. In the case of cosmic strings formed at the end of inflation in the context of grand unified theories, these results challenge simple inflationary models.

Constraints on Cosmic Strings Using Data from the Third Advanced LIGO-Virgo Observing Run

We search for gravitational-wave signals produced by cosmic strings in the Advanced LIGO and Virgo full O3 dataset. Search results are presented for gravitational waves produced by cosmic string loop features such as cusps, kinks, and, for the first time, kink-kink collisions. A template-based search for short-duration transient signals does not yield a detection. We also use the stochastic gravitational-wave background energy density upper limits derived from the O3 data to constrain the cosmic string tension Gμ as a function of the number of kinks, or the number of cusps, for two cosmic string loop distribution models. Additionally, we develop and test a third model that interpolates between these two models. Our results improve upon the previous LIGO-Virgo constraints on Gμ by 1 to 2 orders of magnitude depending on the model that is tested. In particular, for the one-loop distribution model, we set the most competitive constraints to date: Gμ≲4×10^{-15}. In the case of cosmic strings formed at the end of inflation in the context of grand unified theories, these results challenge simple inflationary models.

GW190521: A Binary Black Hole Merger with a Total Mass of 150 M_{⊙}

On May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of 85_{-14}^{+21}  M_{⊙} and 66_{-18}^{+17}  M_{⊙} (90% credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, with only a 0.32% probability of being below 65  M_{⊙}. We calculate the mass of the remnant to be 142_{-16}^{+28}  M_{⊙}, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is 5.3_{-2.6}^{+2.4}  Gpc, corresponding to a redshift of 0.82_{-0.34}^{+0.28}. The inferred rate of mergers similar to GW190521 is 0.13_{-0.11}^{+0.30}  Gpc^{-3} yr^{-1}.

Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA

We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron star-black hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. During O3, the median localization volume (90% credible region) is expected to be on the order of 10 5 , 10 6 , 10 7 Mpc 3 for binary neutron star, neutron star-black hole, and binary black hole systems, respectively. The localization volume in O4 is expected to be about a factor two smaller than in O3. We predict a detection count of 1 - 1 + 12 ( 10 - 10 + 52 ) for binary neutron star mergers, of 0 - 0 + 19 ( 1 - 1 + 91 ) for neutron star-black hole mergers, and 17 - 11 + 22 ( 79 - 44 + 89 ) for binary black hole mergers in a one-calendar-year observing run of the HLV network during O3 (HLVK network during O4). We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers.

Search for Subsolar Mass Ultracompact Binaries in Advanced LIGO's Second Observing Run

We present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO's second observing run. In contrast to a previous search of Advanced LIGO data from the first observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between 0.2  M_{⊙}-1.0  M_{⊙}. We use the null result to constrain the binary merger rate of (0.2  M_{⊙}, 0.2  M_{⊙}) binaries to be less than 3.7×10^{5}  Gpc^{-3} yr^{-1} and the binary merger rate of (1.0  M_{⊙}, 1.0  M_{⊙}) binaries to be less than 5.2×10^{3}  Gpc^{-3} yr^{-1}. Subsolar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with subsolar masses. Assuming a particular primordial black hole (PBH) formation model, we constrain a population of merging 0.2  M_{⊙} black holes to account for less than 16% of the dark matter density and a population of merging 1.0  M_{⊙} black holes to account for less than 2% of the dark matter density. We discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict subsolar mass binaries.

GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence

We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03:38:53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5σ. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4_{-0.9}^{+0.7}×10^{-22}. The inferred source-frame initial black hole masses are 14.2_{-3.7}^{+8.3}M_{⊙} and 7.5_{-2.3}^{+2.3}M_{⊙}, and the final black hole mass is 20.8_{-1.7}^{+6.1}M_{⊙}. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440_{-190}^{+180}  Mpc corresponding to a redshift of 0.09_{-0.04}^{+0.03}. All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity.

Observation of Gravitational Waves from a Binary Black Hole Merger

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

Specialty of principal care physician and Medicare expenditures in patients with coronary artery disease: impact of comorbidity and severity

OBJECTIVE

To explore differences in expenditures for elderly patients with acute and chronic coronary artery disease according to the specialty of the principal care physician.

STUDY DESIGN

Retrospective analysis of Medicare claims.

PATIENTS AND METHODS

A total of 250,514 patients with coronary artery disease (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] codes 410-414) were drawn from a national random sample of 1992 Medicare expenditures. Patients were classified by the physician type with the highest number of Medicare Part B outpatient claims into a cardiologist group and a generalist group. The outcome was mean total expenditures, stratifying (1) by comorbidity as measured by the modified Charlson Index and (2) by severity defined as the proportion of patients with acute myocardial infarction or unstable angina.

RESULTS

Those patients in the cardiologist group had lower comorbidity and higher severity than those in the generalist group. Overall mean expenditures were significantly higher for the cardiologist group than for the generalist group ($7658 vs $6047; P < .001). These differences in mean expenditures were evident at each level of comorbidity. However, when stratified by severity of diagnosis, differences were seen predominantly in those with acute diagnoses. For those with either acute myocardial infarction or unstable angina, the mean expenditures were higher for the cardiologist group than for the combined generalist group ($15,378 vs $12,260; P < .001); however, the mean expenditures for those with only chronic conditions were similar ($4856 vs $4745; P = .53).

CONCLUSION

Expenditures were higher when cardiologists were the principal care physicians treating patients with acute disease but not chronic disease.

Perioperative- and long-term mortality rates after major vascular surgery: the relationship to preoperative testing in the medicare population

Debate continues regarding the value of cardiovascular testing and coronary revascularization before major vascular surgery. Whereas recent guidelines have advocated selective preoperative testing, several authors have suggested that it is no longer necessary in an era of low perioperative cardiac morbidity and mortality. We used data from a random sample of Medicare beneficiaries to determine the mortality rate after vascular surgery, based on the use of preoperative cardiac testing. A 5% nationally random sample of the aged Medicare population for the final 6 mo of 1991 and first 11 mo of 1992 was used to identify a cohort of patients who underwent elective infrainguinal or abdominal aortic reconstructive surgery. Use within the first 6 mo of 1991 was reviewed to determine if preoperative noninvasive cardiovascular imaging or coronary revascularization was performed. Thirty-day (perioperative) and 1-yr mortalities were assessed. Perioperative mortality was significantly increased for aortic surgery (209 of 2865 or 7.3%), compared with infrainguinal surgery (232 of 4030 or 5.8%); however, 1-yr mortality was significantly increased for infrainguinal surgery (16.3% vs 11.3%, P < 0.05). Stress testing, with or without coronary revascularization, was associated with improved short-and long-term survival in aortic surgery. The use of stress testing with coronary revascularization was not associated with reduced perioperative mortality after infrainguinal surgery. Stress testing alone was associated with reduced long-term mortality in patients undergoing infrainguinal revascularization.

IMPLICATIONS

Analysis of the Medicare Claims database suggests that vascular surgery is associated with substantial perioperative and long-term mortality. The reduced long-term mortality in patients who had previously undergone preoperative testing and coronary revascularization reinforces the need for a prospective evaluation of these practices.

Predicting expenditures for Medicare beneficiaries with diabetes. A prospective cohort study from 1994 to 1996

OBJECTIVE

To describe health care expenditures and utilization patterns among older adults with diabetes and to examine factors associated with expenditures over a 3-year period.

RESEARCH DESIGN AND METHODS

We conducted a prospective cohort study of health care expenditures and utilization by diabetic patients from a random nationwide sample of aged Medicare beneficiaries from 1994 to 1996. All services covered by the Medicare program were examined. Multivariate regression was used to assess the contribution of patient characteristics in 1994 on Part B, inpatient, and total expenditures in 1995 and 1996.

RESULTS

Per capita expenditures for beneficiaries with diabetes (n = 169,613) were 1.7 times greater than those for those beneficiaries without diabetes (n = 968,832) in 1994. This ratio remained fairly constant over the 2 years of follow-up. Expenditures for beneficiaries with diabetes were highly skewed. However, few of these individuals remained in the highest expenditure quintile over the 2 years of follow-up. Using multiple regression analysis to adjust for demographic and clinical characteristics, we were able to explain 7% of the variation in total expenditures in 1995 and 6% of the variation in 1996. Using the same model, we were able to explain 10.7% of the variation in Part B expenditures in 1995 and 8% in 1996.

CONCLUSIONS

Beneficiaries with diabetes are consistently more expensive than beneficiaries without diabetes. Demographic and clinical factors at baseline are able to predict only a small portion of future expenditures among this population, and the most expensive patients in one year were often not the most expensive in subsequent years. More work is necessary to assure equitable risk adjustment in the calculation of capitation rates for health plans and practitioners who specialize in the care of individuals with diabetes.

Capitation for cardiologists: accepting risk for coronary artery disease under managed care

Patients with chronic disease may be excluded from capitated managed care plans due to higher than average expected costs. In an attempt to remedy this inequity, one type of risk adjustment technique proposes to set separate capitation rates for certain chronic illnesses, including coronary artery disease (CAD). Cardiologists, who increasingly are requested to accept capitation, will benefit from understanding the impact of using clinical factors as opposed to using demographic factors to set capitation rates. Using a 5% national random sample of the 1992 Medicare population, we determined mean annual expenditures and variation in expenditures of individuals with CAD. We compared the use of 2 demographic factors currently used for capitation rate adjustment (age and gender) with 2 factors not currently used--3-digit International Classification of Disease (ICD-9) code (a measure for severity) and Charlson index (a measure for comorbidity). Mean annual expenditures for individuals with CAD were more than double mean annual expenditures for the general Medicare population ($6,944 vs $3,247). Among individuals with CAD, mean expenditures of subgroups defined by both age and gender ranged from $6,205 to $7,724. In comparison, stratifying by measures of severity and comorbidity identified subgroups with lower and higher mean expenditures, producing a range of $1,702 to $19,959. Substantial variation of expenditures for individuals within subgroups defined by severity and comorbidity remained, with few patients having substantially higher expenditures than the rest. When capitation rates are set with the use of demographic factors alone, patients may be subjected to risk selection and physicians to financial loss. Using clinical measures may decrease the incentive for patient risk selection, but substantial financial risk to physicians would remain, because of a relatively few patients with high expenditures (or costs).

Lung management with perfluorocarbon liquid ventilation improves pulmonary function and gas exchange during extracorporeal membrane oxygenation (ECMO)

We investigated whether pulmonary function and gas exchange would improve with liquid perfluorocarbon ventilation (LV) during ECMO for severe respiratory failure. Lung injury was induced in 11 young sheep 15.1 +/- 3.7 kg in weight utilizing right atrial injection of 0.07 cc/kg oleic acid followed by saline pulmonary lavage. When (A-a)DO2 > or = 600 mmHg and PaO2 < or = 50 mmHg with FiO2 = 1.0, ECMO was instituted. Animals were then ventilated with either standard ECMO "lung rest" gas ventilator settings (ECMO, n = 5) or with "total" liquid ventilation at standard ventilator device settings (LIQ-ECMO, n = 6) utilizing perflubron (perfluooctyl bromide, Liquivent; Alliance Pharmaceutical Corp.). After 3 hours on ECMO, pulmonary physiologic shunt decreased (ECMO = 88 +/- 11% vs LIQ-ECMO = 31 +/- 1%; p < .001) and pulmonary compliance increased (ECMO = 0.50 +/- 0.06 cc/cmH2O/kg vs. LIQ-ECMO = 1.04 +/- 0.19 cc/cmH2O/kg; p < .001). The ECMO flow rate required to maintain the PaO2 in the 50-80 mmHg range was decreased significantly (ECMO = 116 +/- 14 ml/kg/min vs. LIQ-ECMO = 14 +/- 5 ml/kg/min; p < .001). In this model requiring extracorporeal support for severe respiratory failure, lung management with liquid ventilation improves pulmonary function and gas exchange.

Theoretical model of ventricular interdependence: pericardial effects

One ventricle can influence the filling characteristics of the opposite ventricle directly through the myocardium and indirectly through the pericardium. Based on definitions of compliances and volumes, we developed a theoretical analysis that indicated that the magnitude of interdependence was related to the relative compliances of the left and right ventricular free walls, septum, and pericardium. This analysis was verified in postmortem canine hearts. Balloons were inserted into each ventricle, and left ventricle pressure (delta Pl) and volume (delta Vl) changes caused by increasing right ventricular pressure (delta Pr) and volume (delta Vr) or pericardial pressure (delta Pp) were recorded. For delta Pl/delta Pr, delta Pl/delta Pp, delta Pl/delta Vr, delta Vl/delta Pr, delta Vl/delta Pp, and delta Vl/delta Vr measurements, the standard error of estimates was small and the predicted and measured values were significantly related (P less than 0.05); the values were 0.88 +/- 0.16, 0.87 +/- 0.17, 0.93 +/- 0.05, 0.95 +/- 0.09, 0.96 +/- 0.05, and 0.96 +/- 0.04, respectively. These coupling coefficients (delta Pl/delta Pr, delta Pl/delta Pp, etc.) a direct measurement of interdependence, indicated that pericardial-to-ventricular coupling is greater than ventricular-ventricular coupling (delta Pl/delta Pp greater than delta Pl/delta Pr, 0.91 +/- 0.09 vs. 0.23 +/- 0.09, P less than 0.01; delta Vl/delta Pp greater than delta Vl/delta Pr, -1.04 +/- 0.35 vs. -0.19 +/- 0.05, P less than 0.05). This study, by developing a theoretical analysis and by direct measurements, provides a better understanding of ventricular interdependence and may help to predict effects of cardiac tamponade and constrictive pericarditis on ventricular interdependence.

Predictive changes in ventricular interdependence

Based on the balance of forces across the interventricular septum, we developed a theoretical analysis to explain how one ventricle can directly influence the filling characteristics of the other ventricle. The analysis indicated that the pressure and volume transfer were related to the relative compliances of the interventricular septum and ventricular free walls. The present study examined whether the theoretical analysis could be used to predict changes in ventricular interdependence caused by altering regional compliance. To examine this hypothesis, hearts were removed from 18 dogs and placed in cool cardioplegic solution. Balloons were inserted into each ventricle, and the left and right pressure (delta P1, delta Pr) and volume (delta V1, delta Vr) changes caused by changing the pressure and volume of the other ventricle were recorded. After the initial measurements, acute changes in left ventricular free wall compliance (n = 6), septal compliance (n = 6), and right ventricular free wall compliance (n = 6) were induced by glutaraldehyde injections. As predicted by the theoretical analysis, decreasing left ventricular free wall compliance increased delta P1/delta Pr, delta P1/delta Vr, delta Pr/delta V1, and delta Vr/delta V1 significantly (P less than 0.05) by 89 +/- 15, 155 +/- 33, 282 +/- 65, and 112 +/- 22% (mean +/- SEM), respectively. Decreasing septal compliance decreases delta P1/delta Pr, delta V1/delta Pr, delta V1/delta Vr, delta Pr/delta P1, delta Vr/delta P1, and delta Vr/delta V1 significantly (P less than 0.05) by 48 +/- 7, 71 +/- 10, 69 +/- 14, 48 +/- 7, 62 +/- 8, and 57 +/- 13%, respectively. Decreasing right ventricular free wall compliance increased delta P1/delta Vr, delta V1/delta Vr, delta Pr/delta P1, and delta Pr/delta V1 significantly (P less than 0.05) by 97 +/- 25, 79 +/- 20, 57 +/- 18, and 59 +/- 23%, respectively. Furthermore, these alterations in ventricular coupling were predictable: The actual and predicted percentage changes in the transfer functions were in close agreement. The results of these studies show predictable alterations in the mechanical coupling between the ventricles following changes in right ventricular, septal, and left ventricular free wall compliances.

A theoretical and experimental model of ventricular interdependence

Because of the close anatomical association between the ventricles, the volume of one ventricle can directly affect the volume and pressure within the other ventricle. To study the mechanical coupling between the ventricles, we modeled the right and left ventricles as a two-compartment model with right wall (Crw), septal (Cs), and left wall (Clw) compliances. Based on the balances of forces across the septum, four equations were obtained to predict the transfer of pressure (P) and volume (V) information from one ventricle to another. The validity of the theoretical analysis was tested first in a physical model and then in a post-mortem heart preparation. The standard errors of estimate comparing the predicted to measured values were low for both the physical model and the post-mortem heart data. All values were significantly related (P less than 0.05) with r greater than 0.89. The results show excellent correlation between predicted and measured values. This model provides a better understanding of ventricular interdependence and may help to predict effects of hypertrophy and/or myocardial ischemia on ventricular interdependence.

Effect of external inspiratory loading on ventilation of premature infants

The ventilatory response of 11 growing premature infants to external inspiratory resistive loads was evaluated. Air flow, tidal volume, minute ventilation, inspiratory duration and total breath duration were measured before and after application of a flow resistive load. A significant (P less than 0.001) immediate decrease in minute ventilation and tidal volume was observed in all infants after load application. Minute ventilation and tidal volume remained decreased throughout the 10-min study period. Minute ventilation and tidal volume for the group decreased to 48 and 50% of control mean value, respectively. In addition, there was a significant (P less than 0.001) sustained increase in inspiratory time resulting in an increase in the ratio of inspiratory time/total respiratory time.