Defense attorney Jack McMahon has argued that Mongar hid respiratory problems that made her more vulnerable to the effects of Demerol.
Mongar, a native of Bhutan, lived for 20 years in a refugee settlement camp in Nepal before immigrating with her family to the United States four months before she died.
Collins conceded that Mongar's lungs showed carbon particles but said it was the normal soot inhaled by any person, not sign of a disease such as black lung. Otherwise, Collins said, Mongar's lungs were normal.
Questioned by Assistant District Attorney Edward Cameron, Collins said in the Common Pleas Court jury hearing of Gosnell's murder trial that Mongar died when her heart stopped, and her brain died because of lack of oxygen. Collins said the most likely cause was the excessive amount of Demerol found in blood drawn during her autopsy.
Collins will continue to be questioned by McMahon when the trial resumes Thursday, including about why Collins' early drafts of his autopsy report on Mongar tentatively concluded that her death was accidental.
On Tuesday, a toxicologist testified that Mongar was given far more Demerol than her patient records showed.
Timothy Rohrig, a forensic toxicologist and director of the Sedgwick County (Kan.) Regional Forensic Science Center, testified that records from Gosnell's clinic showed Mongar had been administered a total of 150 milligrams of Demerol in the 24 hours before the abortion.
Rohrig said clinic records were inconsistent with the 710 micrograms of Demerol found in a blood sample taken during Mongar's autopsy.
Rohrig testified that there was no way 710 micrograms could remain in her blood shortly after death if she had only been given 150 milligrams.
"It was more than 150 and probably a lot more than 150," Rohrig testified.
In addition to the charge involving Mongar's death, Gosnell is charged with seven counts of first-degree murder in the deaths of newborns whose spines were snipped with scissors after late-term abortions. He faces the death penalty if the jury finds him guilty.
Also on trial is Eileen O'Neill, 52, of Phoenixville, an unlicensed medical school graduate who worked as a doctor in Gosnell's clinic. She is not charged with performing abortions.
Contact Joseph A. Slobodzian at 215-854-2985, firstname.lastname@example.org, or on Twitter @joeslobo.